Humidification system and positive airway pressure apparatus incorporating same

ABSTRACT

Systems, apparatus, and methods for providing humidity in a positive airway pressure (PAP) device. In one embodiment, a humidifier is configured to periodically provide vapor to a flow of pressurized gas to produce flows of pressurized gas with added humidity. Each of the flows of pressurized gas with added humidity may be timed to reach a user interface primarily during a first portion of a breath cycle (e.g., during inspiration). Portions of the flow of pressurized gas that reach the user interface during a second portion of the breath cycle (e.g., during expiration) may include little or no added humidity.

RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Application No.61/916,959, filed Dec. 17, 2013, which is incorporated herein byreference in its entirety.

Embodiments described herein relate generally to positive airwaypressure apparatus and systems, and, more particularly, to systems andmethods adapted to humidify a gas (such as air) delivered by thepositive airway pressure apparatus.

BACKGROUND

Positive airway pressure (PAP) therapies are frequently used in thetreatment of, among other ailments, obstructive sleep apnea, asthma,bronchitis, chronic obstructive pulmonary disease, snoring, andcongestive heart failure. These therapies typically provide a flow offluid (e.g., typically a gas such as air, but may be most any gas orgas-vapor mixture that may or may not include therapeutic agents such asoxygen, water, or medicinal vapors) to pressurize the airway of a userto a pressure in the range of 4-30 centimeters (cm) of water (e.g.,often about 4-20 cm water) or more.

Depending upon the particular therapy, a variable or a constant pressuremay be administered to the user to reduce or eliminate airway occlusions(or to otherwise treat acute or chronic respiratory failure) thatnecessitated the use of the therapy. For instance, continuous positiveairway pressure (CPAP) may provide a generally continuous pressurethroughout the user's breathing cycle. Bi-level positive airway pressure(Bi-PAP) may provide at least two different pressures in coordinationwith the user's inhalation and exhalation efforts. In more advancedsystems, auto-titration positive airway pressure (Auto-PAP) systems mayregulate the therapy pressure based on the level of breathing assistancethe user may require at any given point during a breath.

Regardless of the particular therapy, these positive airway pressure(PAP) systems typically include at least a blower unit and a userinterface or mask. A delivery hose may connect the blower unit to themask, wherein the hose and mask together define a gas delivery conduitbetween the blower unit and the user.

The mask may be configured to secure relative to the user's head in sucha way as to form a generally air-tight seal with the user's airway(e.g., seal about the face, nares, and/or mouth). As a result, theblower unit may generate a flow of pressurized gas that is delivered tothe airway via the delivery conduit.

A humidifier for humidifying the gas provided by the blower unit mayalso be provided. PAP humidifiers typically include a heated waterreservoir containing a volume of water with a relatively large surfacearea. The reservoir is positioned between the blower unit and the mask.Gas from the blower unit may pass over the reservoir, where the gascollects evaporating water. The gas with the now-entrained moisture isthen, via the delivery conduit, provided to the user.

SUMMARY

In one embodiment, a positive airway pressure apparatus is provided thatincludes: a flow generator comprising a housing containing a blower, theblower adapted to produce a flow of pressurized gas; a user interfaceadapted to communicate the flow of pressurized gas to an airway during abreath cycle; and an elongate delivery tube positioned between the flowgenerator and the user interface, the delivery tube adapted tocommunicate the flow of pressurized gas from the blower to the userinterface. The apparatus may also include a humidifier defining anoutlet that is in communication with the flow of pressurized gas,wherein the humidifier has a vaporizing device and a water source, theoutlet located between the blower and the delivery tube. An electricalpower source may be provided and adapted to provide electrical power tothe humidifier. A controller in communication with both the vaporizingdevice and the power source is also provided. The controller is adaptedto automatically modulate the electrical power provided to thehumidifier during the breath cycle, wherein the electrical power ismodulated in proportion to a flow rate of the flow of pressurized gassuch that the humidifier adds water vapor at a rate that maintains anear constant humidity level in the flow of pressurized gas during thebreath cycle.

In another embodiment, a positive airway pressure apparatus is providedthat includes: a flow generator having a housing containing a blower,the blower adapted to produce a flow of pressurized gas at a variableflow rate; a user interface adapted to communicate the flow ofpressurized gas to an airway during a target breath cycle; and anelongate delivery tube positioned between the flow generator and theuser interface, the delivery tube adapted to communicate the flow ofpressurized gas from the blower to the user interface. A humidifier mayalso be provided and includes a vaporizing device having an outlet incommunication with the flow of pressurized gas, wherein the outlet islocated upstream from the user interface. An electrical power source isadapted to provide electrical power to the vaporizing device. Acontroller in communication with both the power source and thevaporizing device is also provided. The controller is adapted to providethe electrical power to the vaporizing device during a power intervalsuch that the vaporizing device introduces water vapor into aninspiration portion of the flow of pressurized gas, during the powerinterval, to produce a flow of pressurized gas with added humidity. Astart time and duration of the power interval are selected or calculatedsuch that the flow of pressurized gas with added humidity arrives at theuser interface beginning at or near an onset of an inspiratory phase ofthe target breath cycle and lasts for most or all of the inspiratoryphase of the target breath cycle.

In yet another embodiment, a method for adding humidity to gas deliveredby a positive airway pressure apparatus is provided. The methodincludes: producing, with a blower, a flow of pressurized gas at avariable flow rate; transporting the flow of pressurized gas from theblower to a user interface via a delivery tube positioned between theblower and the user interface; and detecting, with a controller, one orboth of an inspiratory phase and an expiratory phase of one or morebreath cycles. The method further includes introducing, during a powerinterval, humidity into a portion of the flow of pressurized gas toproduce a discrete flow of pressurized gas with added humidity. Thehumidity is introduced by a vaporizing device having an outlet proximatethe blower and in communication with the flow of pressurized gas. Themethod also includes determining, automatically with the controller, astart time and duration of the power interval so that the flow ofpressurized gas with added humidity reaches the user interface at ornear an onset of an inspiratory phase of a current or future breathcycle and ends at or near an end of the inspiratory phase, or at or nearan onset of an expiratory phase, of the current or future breath cycle.

In still yet another embodiment, a method for adding humidity to gasprovided by a positive airway pressure (PAP) apparatus is provided. Themethod includes: producing a continuous and variable flow of pressurizedgas with a blower; transporting the flow of pressurized gas from theblower to a user interface via a delivery tube positioned between theblower and the user interface; and predicting, automatically with a PAPcontroller, a start time and duration of an inspiratory phase of atarget breath cycle based upon an analysis of a current or a precedingbreath cycle. The method also includes calculating or selecting,automatically with a humidification controller, a delay time andduration of a power interval, and providing power, under control of thehumidification controller, to a vaporizing device after expiration ofthe power interval delay time, wherein the power lasts for the powerinterval duration. The vaporizing device is located proximate an outletof the blower and is in communication with the flow of pressurized gas.The method also includes introducing humidity with the vaporizing deviceinto the flow of pressurized gas during the power interval duration toproduce a flow of pressurized gas with added humidity that reaches theuser interface at or near an onset of the inspiratory phase of thetarget breath cycle and terminates at or near a beginning of anexpiratory phase of the target breath cycle.

The above summary is not intended to describe each embodiment or everyimplementation. Rather, a more complete understanding of illustrativeembodiments will become apparent and appreciated by reference to thefollowing Detailed Description of Exemplary Embodiments and claims inview of the accompanying figures of the drawing.

BRIEF DESCRIPTION OF THE VIEWS OF THE DRAWING

Exemplary embodiments will be further described with reference to thefigures of the drawing, wherein:

FIG. 1 is a diagrammatic illustration of a positive airway pressure(PAP) apparatus incorporating a conventional heated (e.g., watersurface) humidifier;

FIG. 2 is a diagrammatic illustration of an exemplary PAP apparatusincorporating a humidification system in accordance with one embodimentof this disclosure;

FIG. 3 is a diagrammatic, partial illustration of an exemplary PAPapparatus incorporating a humidification system in accordance withanother embodiment;

FIG. 4 is an enlarged diagrammatic view of a PAP apparatus having ahumidification system in accordance with yet another embodiment;

FIG. 5 is an enlarged view of a vaporizing device in accordance with oneexemplary embodiment;

FIG. 6 is a diagrammatic section view of a delivery tube or conduit ofthe exemplary apparatus of FIG. 4 illustrating pulses or intervals ofadded humidity being provided to a flow of pressurized gas provided bythe apparatus;

FIG. 7 is a front perspective view of a flow generator housing of a PAPapparatus in accordance with another embodiment of this disclosure;

FIG. 8 is a front perspective view of the exemplary housing of FIG. 7partially exploded;

FIG. 9 is a rear perspective view of the exemplary housing of FIG. 7partial exploded;

FIG. 10 is a side elevation view of the exemplary housing of FIG. 7partially exploded;

FIG. 11 is an exploded view of the exemplary housing of FIG. 7;

FIG. 12 is a section view taken along line 12-12 of FIG. 7;

FIG. 13 is an exploded perspective view of a humidifier in accordancewith one embodiment;

FIG. 14 is an assembled section view of the humidifier of FIG. 13;

FIG. 15 is a graph of electrical power (watts) used versus watervaporized per minute (cubic centimeters/minute) for a humidifier inaccordance with embodiments of the present disclosure;

FIG. 16 illustrates a method of operating a PAP apparatus under acontinuous modulation humidification mode in accordance with oneembodiment;

FIG. 17 illustrates a method of operating a PAP apparatus under adiscontinuous humidification mode in accordance with one embodiment;

FIG. 18 illustrates a method of simulating flow dynamics in a PAPapparatus;

FIG. 19 illustrates a method for providing continuous humidificationmodulated in accordance with the flow dynamics determined by the methodof FIG. 18;

FIG. 20 illustrates a method for providing discontinuous humidificationmodulated in accordance with the flow dynamics determined by the methodof FIG. 18;

FIG. 21 illustrates a method for predicting humidification timing inaccordance with one embodiment of the disclosure; and

FIGS. 22A-22C are plots illustrating Flow versus Time and Power versusTime for simulated breathing scenarios, wherein the breathing scenariosare generally identical (e.g., same tidal volume) except for varying aPAP system pressure and a breath rate, wherein: FIG. 22A represents asystem pressure of 20 centimeters (cm) of water and a breath rate of 10breaths/minute; FIG. 22B represents a system pressure of 4 cm of waterand a breath rate of 10 breaths/minute; and FIG. 22C represents a systempressure of 4 cm of water and a breath rate of 15 breaths/minute.

The figures are rendered primarily for clarity and, as a result, are notnecessarily drawn to scale. Moreover, various structure/components,including but not limited to fasteners, electrical components (wiring,cables, etc.), and the like may be shown diagrammatically or removedfrom some or all of the views to better illustrate aspects of thedepicted embodiments, or where inclusion of such structure/components isnot necessary to an understanding of the various exemplary embodimentsdescribed herein. The lack of illustration/description of suchstructure/components in a particular figure is, however, not to beinterpreted as limiting the scope of the various embodiments in any way.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the following detailed description of illustrative embodiments,reference is made to the accompanying figures of the drawing which forma part hereof. It is to be understood that other embodiments, which maynot be specifically described and/or illustrated herein, are alsocontemplated.

All headings provided herein are for the convenience of the reader andshould not be used to limit the meaning of any text that follows theheading, unless so specified. Moreover, unless otherwise indicated, allnumbers expressing quantities, and all terms expressingdirection/orientation (e.g., vertical, horizontal, parallel,perpendicular, etc.) in the specification and claims are to beunderstood as being modified in all instances by the term “about.”

Embodiments described herein are directed to positive airway pressure(PAP) apparatus and systems incorporating a humidifier, and to methodsof adding humidity to gas provided by a PAP apparatus. Exemplary PAPsystems, like those described herein, are adapted to modulate deliveryof humidity in proportion to a rate of flow of pressurized gas producedby the PAP apparatus so that a generally constant level of humidity isprovided to the user during an inspiration portion of each breath cycle.In other embodiments, the PAP apparatus may deliver added humidity to aportion of the flow of pressurized gas that reaches a user interface(attached to the user) during a portion of the breath cycle (e.g.,during inspiration), and potentially reduce or even suspend providingthe added humidity to another portion of the flow of pressurized gasthat reaches the user interface during a second portion of the breathcycle (e.g., during expiration). As a result, some embodiments usinghumidifiers like those described herein may provide the user with agenerally constant level of humidity during inspiration, regardless ofchanges in a rate of the flow of pressurized gas, over the course of thetreatment period. Moreover, in some embodiments, the PAP apparatus(e.g., humidifier) may vaporize only a volume of water needed to providea desired target humidity level at the user interface primarily duringinspiration. In still other embodiments, the introduction of addedhumidity to the flow of pressurized gas may occur remotely from the userinterface, but be timed to reach the user interface at the expected orpredicted time of inspiration.

As further described below, exemplary humidifiers as described hereinmay humidify gas within the PAP apparatus by utilizing a vaporizingdevice that vaporizes water when the device is electrically powered(e.g., when electrical power is provided to a moisture transfer orvaporizing element of the vaporizing device) and reduces or terminatesvaporization when power is correspondingly reduced or terminated.Moreover, a rate of vaporization and the volume of water per unit oftime that is vaporized may be dependent upon the level of power providedto the device such that modulating power to the vaporizing device mayproportionally modulate the rate of vapor produced.

By providing added humidity proportional to the flow of pressurized gasduring at least a portion of the breath cycle, the volume of liquid(e.g., water) required, as well as the energy necessary to convert theliquid to vapor, may be less than that required for conventional (e.g.,heated water surface humidifiers such as system 50 of FIG. 1) PAPhumidifiers. The size of the humidifier reservoir, and the powerrequired to convert the liquid to vapor, may be correspondingly reduced.Moreover, embodiments of the present disclosure may provide increasedhumidification levels using reservoirs of similar size to conventionalheated water surface humidifiers.

As used herein, the terms “PAP,” “PAP system,” “PAP apparatus,” etc.refer to positive airway pressure treatment systems for use in treatinga variety of respiratory conditions including but not limited toobstructive sleep apnea (OSA), asthma, bronchitis, chronic obstructivepulmonary disease (COPD), pneumonia, congestive heart failure, andsnoring. Such PAP systems may be adapted for use on both stationary andambulatory users, including applications for non-invasively ventilatingpatients having restrictive lung disease or hypoventilation syndromesusing bi-level positive airway pressure (Bi-PAP) therapy, or adaptiveservo-ventilation for the treatment of complex sleep apnea. PAP systemsmay not include, and may be differentiated from, critical careventilation, wherein the upper airway is completely bypassed andventilation occurs via a tracheostomy. In the case of critical careventilation, relative humidity levels at or near 100% (with airtemperatures at or near body temperature) are common, as compared tolower relative humidity (e.g., 70-95%) typically provided during PAPtherapy (with air temperatures at, near, or somewhat above roomtemperature).

As used herein, the terms “breath cycle” (and “breathing cycle”) referto a respiratory cycle of a user that includes one inspiration (the“inspiratory phase”) followed by one expiration (the “expiratoryphase”). The time it takes to complete one breath cycle is referred toherein as a “breath period.” While breath cycles may vary extensivelydepending on the user and the user's respiratory condition, aflow-versus-time plot of a typical breath cycle may have a generallysinusoidal shape, possibly with different inspiratory and expiratoryperiods or ratios (“I:E ratios”), the latter which typically range from1:1 to 1:2. However, significant deviations from this range can occur,e.g., with patients having respiratory diseases.

It is noted that the terms “comprises” and variations thereof do nothave a limiting meaning where these terms appear in the accompanyingdescription and claims. Further, “a,” “an,” “the,” “at least one,” and“one or more” are used interchangeably herein. Moreover, relative termssuch as “left,” “right,” “front,” “fore,” “forward,” “rear,” “aft,”“rearward,” “top,” “bottom,” “side,” “upper,” “lower,” “above,” “below,”“horizontal,” “vertical,” and the like may be used herein and, if so,are from the perspective observed in the particular figure. These termsare used only to simplify the description, however, and not to limit itsscope in any way.

FIG. 1 illustrates a conventional PAP system 50 with a humidifier havinga heated reservoir 52 positioned between a PAP blower 54 and a userinterface or mask 56. The humidifier may include a heating element 53operable to heat a volume of water 51 contained in the reservoir 52 to apoint where the water evaporates. A rigid or flexible conduit 58 mayconnect an output of the blower 54 to an inlet of the reservoir 52,while a hose 59 typically connects an outlet of the reservoir to aninlet of the mask 56. The hose 59 (or the mask 56) may include anexhaust vent 114. A flow of pressurized gas 60 generated by the blower54 may pass through the humidifier reservoir 52, wherein evaporatingmoisture becomes entrained therein to produce a flow of humidified gas62, which is ultimately provided to the mask 56 by the hose 59.

In a configuration like that of FIG. 1, a relatively large volume ofwater having a correspondingly large surface area is typically providedto permit the pressurized flow of gas 60 produced by the blower 54 togather the desired vapor content as it passes over the water in thereservoir 52 before travelling to the mask 56. While effective, thelarge volume of water, and the energy required to heat such a volume,may result in some inefficiency (e.g., elevated water consumption andpower usage). Moreover, systems like system 50 generally have arelatively slow response time (i.e., the time required to change thereservoir temperature). Accordingly, controlling the vapor content ofthe flow of humidified gas 62 during system operation may be limitedbased upon how quickly the reservoir can be heated or cooled. As aresult, humidification outside of the desired range could occur duringat least a portion of the treatment period. For example, the system 50may provide less that desired humidity levels when PAP pressure and/orflow rate are high. Additionally, such systems may result in increasedflow resistance due to a circuitous airflow path (not shown) used toroute the flow of pressurized gas over the expansive water surface. Suchan airflow path may be of benefit, however, to minimize the chance ofwater leaking, e.g., back into the blower 54 or down the hose 59 to theuser.

With reference to the figures of the drawing, wherein like referencenumerals designate like parts and assemblies throughout the severalviews, an exemplary embodiment of a PAP apparatus 70 in accordance withone embodiment of this disclosure may be configured as diagrammaticallyrepresented in FIG. 2. As shown in this view, the PAP apparatus 70 mayinclude a flow generator having a flow generator housing 84 containing ablower 74, a user interface (mask 76), and a delivery tube 78 positionedbetween the flow generator (blower) and the user interface andoperatively connecting the blower/housing to the mask. The flowgenerator (e.g., blower 74) may be adapted to produce a flow ofpressurized gas (e.g., at a variable flow rate and at a constantpressure regardless of the flow rate), wherein the delivery tube 78 isoperable to transport (communicate) the flow of pressurized gas producedby the blower from an outlet of the blower 74/housing 84 to an inlet ofthe user interface. Once again, the delivery tube 78 or the mask 76 mayinclude a vent 114.

The apparatus 70 may include a humidifier having a moisture transferelement capable of rapidly initiating and terminating moisture deliveryto the flow of pressurized gas (e.g., delivering moisture during a firstportion of a breath cycle and reducing or suspending delivery ofmoisture during a second portion of the same breath cycle). In theembodiments described and illustrated herein, the moisture transferelement may be configured as a capillary force vaporizer (CFV) 73. TheCFV 73 may be configured to introduce/add humidity to a flow ofpressurized gas 80 produced by the blower 74 to create a flow ofpressurized gas with added humidity 82 for delivery to the mask 76. TheCFV 73 may be part of a humidification subsystem 71 of the apparatus 70that also includes a reservoir 72 and a water conveying device 75 (e.g.,a wick or small tube (with or without a water pump)) operable totransport water from the reservoir to the CFV.

In one embodiment, some or all of the humidification subsystem 71 may bephysically separate from the blower 74/housing 84 as shown in FIG. 2(although electrical interconnections may be provided). In otherembodiments, as shown in the partial view of the apparatus 70 in FIG. 3,some or all of the humidification subsystem 71 may be contained withinthe same housing (e.g., flow generator housing 84) that encloses theblower 74. The latter configuration may permit for a more compactdesign, while the former may be more conducive to retrofitting existingPAP apparatus. The embodiment of FIG. 3 may also provide advantages suchas: reduced cost; smaller, unitary housing; integrated electronics(e.g., single printed circuit board (PCB)); elimination of externalinterconnects; and a single power supply. While not illustrated in FIG.3, other embodiments could separate the water reservoir 72 from thehousing 84, e.g., to simplify refilling.

With this general introduction, FIG. 4 illustrates an exemplaryembodiment of a PAP system or apparatus 100 in accordance with anotherembodiment of this disclosure. The apparatus 100 may be similar in manyrespects to the apparatus 70 described above in FIGS. 2 and 3 (e.g., itmay utilize a humidification subsystem incorporating a CFV).

The PAP apparatus 100 may include a flow generator or blower 102 havingan outlet 104 that may be in communication with a first or proximal endof an elongate delivery hose or tube 106 positioned between the flowgenerator (e.g., blower 102) and a user interface or mask 108. In theillustrated embodiment, a T-shaped connector 301 (in cross-hatchedsection) may be located between the outlet 104 and the delivery tube 106for reasons that will become apparent.

A second or distal end of the delivery tube 106 may be connected to aninlet of the user interface 108. The user interface 108 is illustratedgenerically, but is understood to include most any interface that sealseffectively to a user 110 (e.g., about the user's face (nose and/ormouth) or within the user's nares) in such a way that a flow ofpressurized gas delivered to the user interface may be communicated toan airway 112 of the user during treatment (e.g., during one or morebreath cycles). For example, the user interface could be a face maskthat covers one or both of the user's mouth and nose; a nares pillowseal; or any similar device or combination of such devices. Forsimplicity, the user interface may be referred to hereinafter as a“mask” without limitation.

As used herein, the term “gas” is understood to include most any gas orgas-vapor combination. For example, the gas provided by the blower 102may include air, oxygen, water vapor or droplets, medicinal vapor ordroplets, and combinations thereof. For simplicity of description, theterms “air,” “fluid,” and “gas” may be used interchangeably herein.“Pressurized gas,” as used herein, refers to gas at a positive pressurerelative to ambient pressure. “Blower,” as used herein, refers to mostany device or source capable of producing a flow of pressurized gas.

The delivery tube 106 and user interface (mask) 108 may together definea delivery conduit 107 forming a passage that transports or otherwisecommunicates the flow of pressurized gas from the outlet 104 of theblower 102 to the inlet of the mask and then to the airway 112 of theuser 110. The delivery conduit, e.g., delivery tube 106 or mask 108, mayinclude one or more exhaust vents 114. Such vents are known to providewhat is referred to an “intentional leak.” Intentional leak is providedto assist in purging carbon dioxide from the delivery conduit 107 duringthe expiration phase of each breath cycle. In one embodiment, one ormore vents 114 may be included and provide the equivalent of a single,four millimeter (mm) opening (although other leak sized are certainlypossible). In practice, the vent leak may vary widely (e.g., up to sixmm opening) depending on mask type.

To provide the desired flow of pressurized gas within the deliveryconduit 107, the blower 102 may be part of a flow generator having aflow generator or blower housing 103 forming a volute containing animpeller or fan 116. An electric motor 118, such as a brushless DCmotor, may rotate the fan during use. As the fan rotates, it draws gas(e.g., ambient air) in via an inlet 120 of the blower 102/housing 103,where the gas is then compressed by the fan and expelled through theoutlet 104. By controlling the rotational speed of the fan 116, thepressure of the gas within the delivery conduit 107 may be controlled toprovide the desired treatment pressure to the user 110.

The apparatus 100 may further include a gas flow or PAP controller 200that, among other tasks, may modulate or otherwise control a speed ofthe motor 118 (and, accordingly, a speed of the fan 116) to, forexample, produce a variable flow rate at a constant pressure. The PAPcontroller 200 may, in one embodiment, include a microprocessor-basedmotor controller 206. All electrical components may be powered by eitheran onboard electrical power source or supply (e.g., a battery 202) or aremote power supply (AC or DC source) via an electric cord 204. The PAPcontroller 200 may electrically interconnect other components of thesystem 100 as further described herein.

The PAP controller 200 may be contained within the blower housing 103 asshown in FIG. 4. Alternatively, the PAP controller could be housed in aseparate enclosure (not shown).

The PAP apparatus 100 may further include a pressure transducer 128. Inone embodiment, the pressure transducer 128 is located within thehousing 103. For example, in the illustrated embodiment, the pressuretransducer 128 is located within the housing 103 and is connected at ornear the outlet 104 (or, alternatively, connected at most any otherpoint along the delivery conduit 107) via a pressure line or conduit130. The pressure transducer 128 may produce an electrical signalproportional to the actual, measured pressure within the deliveryconduit 107. The pressure signal may then be transmitted to the PAPcontroller 200 via an electrical signal line 132 as illustrated in FIG.4. As further described below, the PAP controller 200 may compare thepressure signal to a commanded pressure and, via closed-loop control,modulate a commanded motor speed to the motor 118 via a command line 208from the motor controller 206. As a result, the apparatus 100 maymaintain a desired pressure in the delivery tube 106/mask 108 regardlessof anticipated variations in flow.

In other embodiments, additional sensors, e.g., a pneumotachometer 134(e.g., a differential pressure transducer placed across a knownrestriction), may also be provided as shown in FIG. 4 (thepneumotachometer may be placed most anywhere in the apparatus 100 (e.g.,anywhere between the air inlet 120 and the mask 108). Thepneumotachometer 134 may provide the PAP controller 200 with anelectrical signal proportional to the instantaneous flow within thedelivery conduit 107 via a sense line 136. Other sensors 135, e.g.,temperature, humidity, etc. may also be provided and electricallyconnect to the PAP controller 200 as indicated (see e.g., line 133).

While described as a pneumotachometer, other devices and/or methods formeasuring or estimating air flow may also be used. For example, otherembodiments may analyze a speed of the motor 118 or the voltage,current, or power draw of the motor.

The exemplary apparatus 100 may, in one embodiment, further include ahumidifier subsystem (“humidifier 300”) as diagrammatically illustratedin FIG. 4. The humidifier 300 may include the vaporizing device (whichmay be a CFV 302), a water source or reservoir 304, and a waterconveying device 306 (e.g., a wick or small tube (again, with or withouta pump)) connecting the water source 304 with the vaporizing device. Thehumidifier (i.e., the vaporizing device), embodiments of which aredescribed in more detail below, may be positioned proximate the blower,e.g., between the blower 102 and the delivery tube 106 (or elsewherealong the delivery conduit 107), such that an outlet 318 of thehumidifier (e.g., of the vaporizing device) is in communication with theflow of pressurized gas produced by the blower 102. While the vaporizingdevice could be located at most any position along the delivery tube106, the mask 108 (either before or after the port 114), or even at orwithin the housing 103 (as further described below), it is, in theillustrated embodiment, positioned between the blower and the deliverytube, e.g., within the T-shaped connector 301. The connector 301 mayinclude a first leg 322 connected to the outlet 104 of the blower102/housing 103, and a second leg 324 connected to the delivery tube 106as shown in FIG. 4. A base leg 326 of the T-shaped connector 301 maythen receive and support the vaporizing device. In one embodiment, aperipheral edge of the vaporizing device (e.g., CFV 302) is sealedagainst an inner surface of the connector 301 such that the flow ofpressurized gas does not escape through the T-shaped connector. In otherembodiments, a pressure equalization port may be positioned between thedelivery conduit 107 and the reservoir 304 to equalize a pressuretherebetween.

When configured as described above, the apparatus 100 places thevaporizing device in communication with the flow of pressurized gas andat or near the outlet 104 of the blower 102/housing 103. Such aconfiguration may simplify the apparatus 100 by shortening fluidconnections between the water reservoir 304 and the vaporizing device.For example, the water source 304 may be located adjacent the blowerhousing 103 as indicated in FIGS. 2 and 4 (or alternatively, within thePAP housing 103 as shown in FIG. 3).

In one embodiment, water 305 contained within the water reservoir 304may be conveyed, via wicking or capillary action, to the vaporizingdevice (e.g., CFV 302) by the water conveying device 306. While soillustrated, other embodiments may utilize a pump (fixed or variabledisplacement, peristaltic, etc.) connected to the water reservoir 304and the vaporizing device to convey water from the former to the latter.In such a configuration, the pump may be activated (e.g., by ahumidification controller 303) to deliver water, via a water line, tothe vaporizing device. In some cases, the water conveying device 306 maysimply be a short, small diameter capillary tube (without a pump). Watermay then be conveyed by the tube via capillary force created by thevaporizing device, as well as capillary forces created by walls of thetube, or by gravity (depending on the position of the reservoir).

Conventional heated humidifiers (see, e.g., FIG. 1) operate by passingall of the PAP-generated gas over the relatively large surface area ofwater in a water reservoir. The entire reservoir of water is then heatedto enhance the amount of water that evaporates into the gas stream. Thiscontinual heating of the water reservoir requires sustained power as itcontinuously humidifies the gas flowing through the tube 62 (regardlessof flow rate of the gas), much of which escapes out the vent 114 ratherthan ultimately making its way to the airway of the user.

Unlike these conventional PAP humidifiers, the humidifier 300 (e.g., thevaporizing device) may, in one embodiment, be a CFV 302 such as thehumidifier element used in the MyPUREMIST model CFV 100 personalhumidification unit distributed by Vapore, LLC. of Concord, Calif., USA.Such CFV devices may convert water into vapor by providing a heating orvaporizing element (e.g., heated surface area) that converts liquid tovapor via both capillary force and phase transition. The effect is thatvapor may be forcefully emitted from the outlet 318 of the vaporizingdevice 302 upon electrically energizing (heating of) the vaporizingdevice. As a result, the PAP apparatus 100 may be able to rapidly andreliably control the vapor output of the CFV throughout the breath cycleto provide the flow of pressurized gas with the desired target humiditylevel. That is, because of the responsive nature of the CFV 302,humidification of the flow of pressurized gas (to produce a flow ofpressurized gas with added humidity) may be precisely controlled duringindividual breath cycles to ensure a constant (or near constant) levelof humidity is provided to the user during inspiration (over the entiretreatment period), even when parameters such as breath rate, breathflow, leak magnitude (intentional or unintentional), tidal volume,and/or pressure changes. Thus, the CFV 302 may require heating only theamount of water that is needed to provide a constant (or near constant)target humidity level to the flow of pressurized gas delivered to theuser interface. In other embodiments, the CFV 302 may add humidity (toreach the desired target humidity level) to only those portions of theflow of pressurized gas that reach the user interface primarily duringthe inspiratory phase of each breath cycle. Accordingly, disadvantagesassociated with conventional humidifiers (e.g., heating of a largereservoir of water, delivering humidified gas to the user interfaceduring the expiratory phase) may be avoided.

In the embodiment illustrated in FIG. 4, the humidifier 300 may includea humidifier housing 311 containing, among other components, thehumidification controller 303 (also referred to herein as “controller”).The humidification controller 303 may be in communication with thevaporizing device (CFV 302) and a power source 313 such that it isoperable to selectively deliver electrical power from the power sourceto the vaporizing device (e.g., during at least a portion of the breathcycle) via a power line 309. The humidifier 300 may include the separatepower source 313 as shown to provide electrical power to the vaporizingdevice and to other components of the humidifier, or the humidifier maydraw its power from the power source (e.g., battery 202 or sourceconnected to cord 204) associated with the housing 103. Thehumidification controller 303 may also be electrically connected to thePAP controller 200 (e.g., via communication line 307) so that signalsand other information regarding breath parameters (e.g., gas pressure,flow rate, and inspiration/expiration parameters) and humidificationdata, may be conveyed to/from the humidification controller. In otherembodiments, some or all aspects of the humidification controller 303and the PAP controller 200 may be incorporated into a single controllermodule (as could be the case with the system illustrated in FIG. 3).Accordingly, as used herein, the term “controller” may be understood toinclude either or both of the PAP controller and the humidificationcontroller.

The humidification controller 303 and/or the PAP controller 200 mayanalyze data to determine various parameters associated with PAPoperation. For example, breath rate, tidal volume, intentional leakflow, gas flow, mask leak flow, inspiratory/expiratory transitions,predictions regarding onset and/or duration of inspiratory phases ofsubsequent (future) breath cycles, algorithm functional constants and/orlookup tables, vaporizing device operating parameters (some of which aredescribed in more detail below), among others, may all be analyzedand/or determined by the humidification controller 303 and/or the PAPcontroller 200. Still yet other parameters regarding operation of thePAP apparatus 100 (or PAP apparatus 70), e.g., volume (e.g., length anddiameter) of the delivery tube 106, mask intentional leak, mask deadspace, and desired humidification level may be user-provided, e.g., viaa control panel or the like located on the housing 103 and/or thehumidifier housing 311. Some of these parameters may be explicitlyentered, while others may be selected from component classifications.For example, instead of entering explicit dimensions for the hose 106and/or mask 108, the user may only be required to select a hose or maskpart number or descriptor (e.g., “A,”, “B,” or “C”). The controller 200(or 303) may then automatically determine intentional leak, hose volume,and other parameters.

The CFV 302 may respond quickly to commands from the controller 303 (orthe controller 200). As a result, exemplary vaporizing devices (e.g.,CFV 302) may be able to modulate vapor delivery to the flow ofpressurized gas to provide, in one embodiment, the flow of pressurizedgas with a generally constant level of humidity (e.g., a continuousmodulation humidification mode) regardless of changes in rate of theflow of the pressurized gas. Moreover, in other embodiments, theapparatus (e.g., vaporizing device) may be able to reduce or evensuspend vapor delivery (e.g., a discontinuous humidification mode) to aportion of the flow of pressurized gas (e.g., the portion that ispresent at the user interface during the expiratory phase of the breathcycle) by reducing or suspending electrical power to the vaporizingdevice, and then resume vapor delivery to another portion of the flow ofpressurized gas (the portion that is present at the user interfaceduring the inspiratory phase).

In either the continuous or discontinuous humidification mode, the totalwater and power required over the treatment period to provide thedesired humidity level to the user during the inspiratory phase of eachbreath cycle (the “target humidity level”) could be reduced as comparedto conventional PAP humidification. In fact, it is contemplated thatsome embodiments of the PAP systems described herein (e.g., apparatus70, 100, and 400) could provide the target humidity level to the user(at least during the inspiratory phase of each breath cycle) over thecourse of a typical treatment period (e.g., 8-10 hours) while using asmaller water reservoir and less power (as compared to conventional PAPhumidifiers).

As an example, a conventional water surface humidifier may have areservoir size of 300-500 cubic centimeters (cc) and require 60-500watts (on average) to adequately deliver a desired humidity level (e.g.,up to 95% relative humidity) over a treatment period of 8 hours. It isbelieved that a PAP apparatus like the apparatus 100 of FIG. 4 (or theapparatus 70 and 400 described herein) having a humidifier like thehumidifier 300 (or humidifier 600 described below) could provide thesame or similar target humidity level to the user during the user'sinspiratory phase for the same treatment period of 8 hours using areservoir size of 150-300 cc with power of 15-45 watts (on average). Asa result, a smaller, more water- and energy-efficient PAP apparatus mayresult. Of course, actual performance of this or any other humidifiercould vary, perhaps significantly, based upon a variety of factorsincluding but not limited to: system pressure; tidal volume; minutevolume; breath rate; flow rate; intentional leak; unintentional leak;desired humidity; and ambient temperature/humidity. For extremeconditions of high pressure (greater than 16 cm water), high intentionalleak (e.g., as may be the case with a full face mask), and largeunintentional leaks, systems like the system 100 (and the systems 70 and400 described herein) could potentially provide higher humidity levelsthan that typically offered by traditional heated humidifiers. Ofcourse, to provide such humidity levels, higher CFV power levels andwater volumes may be needed.

While identified herein as a CFV 302, humidifiers having other types ofmoisture transfer elements now known or later developed that may providesimilar performance/response are also contemplated.

As shown in FIG. 5, the exemplary CFV 302 may form a vaporizing elementthat is an assembly of multiple layers of different porosity. Forexample, the CFV 302 may include a porous member that, in oneembodiment, includes an insulating layer 310 and a vaporizing element312. The porous member may be placed in contact with a heating/ejectionlayer 316. The heating layer may include a heater or heating element(powered by the power line 309) and a heat exchanger 314. Theheating/ejecting layer 316 may include an outlet or opening 318 adaptedto emit pressurized vapor (e.g., into the flow of pressurized gas withinthe delivery conduit 107) from vapor that collects in channels formedbeneath the surface of the heating/ejecting layer. Water may be conveyedto the insulating layer 310 by the water conveying device 306 or viaother mechanisms (e.g., gravity). For more information regardingexemplary CFV constructions, see, e.g., U.S. Pat. App. Pub. No.2010-0142934 and U.S. Pat. Nos. 6,634,864 and 7,942,644.

By delivering power (i.e., electrical current) to the heating/ejectinglayer 316, the temperature of the CFV 302 may be elevated rapidly,permitting vapor to be almost instantaneously produced and forcefullyemitted by the heating/ejecting layer 316 (via the opening 318) into theflow of pressurized gas. Moreover, assuming that adequate liquid isavailable to the vaporizing element 312, the volume of water vaporproduced by the CFV 302 may be directly proportional to the powerdelivered to the CFV. As a result, output of the CFV 302 may bemodulated (by modulating electrical power to the CFV) to accommodatevariations in flow during the breath cycle.

In some embodiments, the controller (e.g., controller 303 or controller200) may be configured to simply monitor a rate of the flow ofpressurized gas and automatically modulate the electrical power to theCFV 302 during the breath cycle. This process may modulate the amount ofwater vapor added in proportion to the flow of pressurized gas tomaintain a generally constant target humidity level in the flow ofpressurized gas (even as the flow of pressurized gas changes) during thebreath cycle and over the treatment period. In other embodiments, thecontroller (303 and/or 200) may further analyze current or previousbreath cycles to predict future breath/humidification needs, and commandthe CFV to provide added humidity primarily to those portions (the“inspiration portions”) of the flow of pressurized gas that will reachthe user interface 108 at or near the onset of the inspiratory phase ofeach breath cycle. In the case of this pulsed or discontinuoushumidification mode of the CFV 302, the system may again provide agenerally constant level of humidity to the patient during theinspiratory phases even as the flow of the pressurized gas changes overthe course of inspiration. FIG. 6 may illustrate exemplary operation ofthis discontinuous humidification mode. Of course, in some embodiments,the CFV 302, under command of the humidification controller 303, maytemporarily provide a higher humidity level (e.g., during peak gas flowsand/or during high levels of inspiration). However, in such cases, thesystem 100 may maintain a general constant average humidity level foreach breath cycle.

FIG. 6 diagrammatically illustrates a section view of the PAP apparatus100 (similar to the PAP apparatus 70 and 400 described elsewhere herein)during operation, e.g., using the humidifier 300 of FIG. 4. As shown inthis view, the delivery conduit 107 (e.g., the delivery tube 106) mayroute the flow of pressurized gas 136 generated by the blower 102 to theuser interface 108. The CFV 302 may, at least in one embodiment,periodically eject water vapor 138 into the flow of pressurized gas 136,whereby the vapor becomes entrained therein to produce periodic,discrete pulses or flows of pressurized gas with added humidity 140carried within the delivery conduit 107 as represented by stippledsections in FIG. 6. Because the vapor produced by the CFV 302 isresponsive to changes in electrical power provided to theheating/ejecting layer 316 (see FIG. 5), the power delivered to the CFV302 to produce each of the flows of pressurized gas with added humidity140 may, in one embodiment, be modulated to maintain relatively constanthumidity as the rate of flow of the pressurized gas increases/decreases.Such changes in rate of flow may occur, for example, during normalinspiration and expiration, when PAP pressure and/or flow rates changedue to unintentional leaks and mask re-sealing (the latter which mayoccur during user movement), and in response to sleep disordered events(e.g., when using an Auto-PAP device).

Power to the CFV 302 may be reduced substantially or suspendedaltogether (in some embodiments) during a portion of the breath cycle toeffectively reduce or even terminate the introduction of additionalhumidity into the flow of pressurized gas 136. As a result, the flow ofpressurized gas may include the pulses or flows of the pressurized gaswith added humidity 140 separated by periods of the flow of pressurizedgas 142 that are non-humidified or “dry” as represented in FIG. 6. Asused herein, the terms “non-humidified” or “dry” may be used to describepressurized gas that lacks additional moisture intentionally provided bythe CFV 302. However, those of skill in the art will appreciate thatthis non-humidified or dry gas may include some vapor content based uponthe ambient gas from which the blower draws, or from residual moisturein the tube 106 or from the CFV 302, the latter resulting from apotentially less-than-instantaneous on/off response of the CFV toapplication of electrical power.

By applying principles in accordance with embodiments as describedherein, the pulses or flows of pressurized gas with added humidity 140may be timed to be delivered to the user interface 108 primarily duringthe inspiratory phase of each breath cycle. That is to say, water vapormay be provided by the CFV 302 to the inspiration portions of the flowof pressurized gas (to produce the flows of pressurized gas with addedhumidity) that are timed to reach the user interface during theinspiratory phase of each breath cycle. Conversely, the flows ofnon-humidified gas 142 may reach the user interface primarily during theexpiratory phase of each breath cycle, or during pauses in breathing.Stated another way, the timing of the interval that produces the flow ofpressurized gas with added humidity may be selected to ensure that theflow of pressurized gas with added humidity reaches the user interface108 generally at or near an onset of the inspiratory phase of a currentor subsequent (e.g., future) breath cycle and lasts for a duration ofthat inspiratory phase. Thus, added humidity to the flow of pressurizedgas reaching the user during the expiratory phase may be reduced,minimized, or even avoided, thereby reducing the total volume of waterrequired over the treatment period as well as reducing the power neededto provide the desired target humidity level to the user.

The timing of the delivery of the flows of pressurized gas with addedhumidity 140 may be complicated in some embodiments by the remotelocation of the humidifier (e.g., the vaporizing device (CFV) 302). Thatis, when the CFV 302 is positioned upstream of the user interface 108 bya distance 320, the flow of pressurized gas with added humidity 140produced by the vaporizing device is delayed, after introduction, inreaching the user interface 108 (e.g., it lags behind the introductionof the added humidity). This delay is dependent on several factorsincluding: the distance 320, the pressure of the flow of pressurized gas136, tidal volume, and breath rate, as well as tube 106/mask 108 volumeand intentional and unintentional leak flow. This delay could be atleast partially alleviated by locating the CFV 302 closer to the userinterface. However, moving the CFV 302 away from the housing 103 couldresult in a less compact design, e.g., power and water would need toextend to the CFV location.

Illustrative apparatus and methods like those described and illustratedherein may address this problem by accurately predicting when the onsetof the next inspiratory phase will begin, and timing a start andduration of a power interval to the vaporizing device 302 to produce thepulses or flows of pressurized gas with added humidity 140. Byaccurately predicting inspiration and timing the power interval basedupon that prediction, the apparatus 100 (or apparatus 70 and 400) maydeliver the flows of pressurized gas with added humidity 140 to the userinterface 108 beginning at the onset of the inspiratory phases andlasting for the duration of the inspiratory phases.

In one embodiment, injecting the humidity into the flow of pressurizedgas may include injecting humidity into the flow of pressurized gasbefore the inspiratory phase of the target breath cycle, e.g., injectingthe humidity during at least a portion of a breath cycle preceding thetarget breath cycle (e.g., the breath cycle for which the humidity is tobe added). Moreover, each injection of humidity may be provided for thepower interval duration (which is estimated or otherwise determined bythe controller 303 or controller 200) to ensure that the added humidityis provided for most or all of the inspiratory phase of each breathcycle. Still further, the power delivered during the power interval maybe modulated by the controller 303 to ensure delivery of a generallycontinuous level of humidity regardless of the flow of gas (i.e., thevapor emitted by the vaporizing device may be proportional to the flowwithin the conduit 107).

While not wishing to be limited to any specific embodiment, the powerinterval start time (also referred to herein as a power interval delaytime) and duration, as well as how electrical power to the CFV will bemodulated, may be determined based on one or more of: a pressure of thepressurized gas; total hose flow (which may include flow attributable toeach of: intentional leak; unintentional leak; and breath cycle flow); abreath rate of the user; inspiratory tidal volume; expiratory volume;I:E ratio; inspiratory and expiratory flow dynamics (e.g., shape andamplitude of the flow curves); start and end times of both inspirationand expiration; time of peak flow during inspiration and expiration;power available to the vaporizing device, a volume of the delivery tubeand the user interface between the outlet of the humidifier and theairway (which is a function of the distance 320); and apower-to-vaporization transfer function of the vaporizing device.

PAP apparatus and methods incorporating CFVs (e.g., apparatus 70, 100,and 400) may offer numerous benefits. For instance, by delivering vaporin proportion to the electrical power or current supplied to the CFV302, humidity added by the CFV may be dynamically adjusted to meet theneeds of a particular user, e.g., based upon actual breath needs.Moreover, as stated elsewhere herein, due to the responsiveness of theCFV 302, power to the CFV may be modulated during vaporization tominimize power and water usage while maintaining a relatively constanttarget humidity level based upon gas flow. In still other embodiments,power to the CFV may be entirely terminated during at least a portion ofone or more breath cycles. As further described below, in embodimentsthat provide this discontinuous humidification, power delivery to andmodulation of the CFV 302 may be initiated based upon a detectedparameter of a breath (e.g., the onset of inspiration or expiration of aprevious breath cycle, a peak inspiratory or expiratory flow, etc.).

FIGS. 7-14 illustrate an exemplary PAP apparatus 400 similar in manyrespects to the PAP apparatus 70 and 100 already described herein. Theapparatus 400 may include a flow generator housing 403 that incorporatesa humidifier subsystem, negating the need for separate humidifierhousing. Aspects of the apparatus 400 (e.g., the housing 403) may beinterchanged with, or combined with, aspects of the PAP apparatus 70 and100 already described herein above. For example, the housing 403 mayreplace the housing 103 (and the humidifier 300) in the apparatus 100 ofFIG. 4 such that the delivery tube 106 and user interface 108 wouldattach directly to an outlet 408 of the housing 403 as shown in FIG. 7.

As further shown in FIG. 7, the housing 403 may be defined by a body 402and a base 404. In one embodiment, the base 404 may be separable fromthe body 402 as shown in FIG. 8 to provide access to a water reservoir406 contained within the base. When assembled, the housing 403 may beadapted to rest upon a horizontal surface such as a tabletop or floor.The housing further defines the outlet 408 adapted to connect to thedelivery tube 106 as already described herein.

The housing 400 may further define an Input/Output (I/O) or controlinterface 410 to permit user input and system feedback regardingoperation of the apparatus 400. In one embodiment, the control interfaceincludes an input device, e.g., directional joystick 412, and an outputdevice, e.g., LCD screen 414. During operation, various operationalparameters may be presented on the LCD screen, whereby the user mayselect and/or alter such parameters by manipulation of the input device.Of course, while shown as a joystick and LCD screen, such aconfiguration is not limiting. For example, a series of discrete knobsor switches, indicator lights, touchscreen interfaces, and the likecould be used alternatively, or in addition, to the joystick and LCDscreen shown. In yet other embodiments, the control interface 410 may beconfigured as a remote computer (e.g., smartphone) that communicates(via wired or wireless protocols) with the housing 403.

FIG. 9 illustrates a rear perspective view of the housing 403 with thebase 404 once again shown exploded from the body 402. As shown in thisview, the housing may include one or more inlet passages 416 to permit ablower (not shown) contained within the housing 403 to draw ambient gasinto the housing. To filter the ambient gas, an air filter cartridge 418supporting air filter media may also be included. The rear side of thehousing 403 as illustrated in FIG. 9 may also provide other features,e.g., on/off switch 420, a connector 422 for DC power connection, aswell as other connectors (e.g., data port).

FIG. 9 also illustrates a lower portion of a humidifier 600. Thehumidifier 600 may extend into the water reservoir 406 (see FIG. 8) viaan opening 424 formed in the base 404. The humidifier 600 is shownremoved from the housing in FIG. 10. As shown in this view, separationof the base 404 from the body 402 may allow removal of the humidifier600 as well as removal of the air filter cartridge 418, e.g., formaintenance.

FIG. 11 is an exploded view of the exemplary housing 403. As shown inthis view, the body 402 may form an open top container into whichcomponents of the apparatus 400 may install. The body 402 may furtherinclude a removable cap portion to cover the open top of the housingonce assembled.

Within the housing 403, a blower assembly or blower 430 may be provided.The blower 430 may include an impeller 431 or fan powered by an electricmotor 433 (see FIG. 12). When the impeller is rotated by the motor, itmay draw ambient gas into a plenum (e.g., through the air filtercartridge 418) where the gas is then compressed and expelled outwardlythrough an outlet 432 of the blower as a flow of pressurized gas. Bycontrolling the speed of the fan, pressure and rate of the flow ofpressurized gas may be controlled. Like the other blowers describedherein, the blower 430 may be able to maintain a sustained pressure evenas the rate of flow of pressurized gas changes (e.g., during breathing).

Various electronics may also be included to provide real time control ofthe blower 430 and other aspects of the apparatus 400. In oneembodiment, these electronics may be incorporated onto a printed circuitboard (PCB) 434. The PCB may include a microprocessor 436, a PAPcontroller 437 (e.g., to control the blower 430), a humidity orhumidification controller 630 (described in more detail below), and amemory unit 438.

The housing 403 may further contain an I/O board 440 that receives inputfrom the joystick 412 and outputs information to the LCD screen 414. TheI/O board 440 is in communication with the PCB 434 to permitbidirectional communication with the components of the PCB 434 and othercomponents of the apparatus. The control interface 410 may allow variousinputs including, for example, the target humidity level desired duringoperation. Such a humidity level may be referred to in relative terms,e.g., the control interface may provide settings 1-10, eachcorresponding to a successively higher target humidity level.

The housing 403 (e.g., the body 402) may also include various seals orcovers to protect system components (e.g., a transparent cover may beprovided over the LCD screen 414). The housing 403 may provide otherseals to ensure that flow through the apparatus is contained. Forexample, an air filter cartridge seal 442 may be provided to ensureambient air flows into the blower 430 and not to unintended areas of thehousing 403.

A gasket 444 may be located at or near the blower outlet 432 between theblower 430 and a humidifier housing 446, the latter adapted to removablyreceive the humidifier 600 as further described below. The humidifierhousing 446 may include an inlet 448 that communicates with the outlet432 of the blower 430, and an outlet 450 that communicates with theoutlet 408 of the housing 403. In one embodiment, a seal 449 may beprovided between the outlet 450 and the outlet 408 to preventpressurized gas from leaking into the housing 403.

The humidifier housing 446 may also include a pressure port 452 adaptedto communicate with a conduit 453 on the blower 430. The conduit 453 mayconnect to a pressure sensor or transducer 454, e.g., located on the PCB434.

FIG. 12 is a diagrammatic section view of the housing 403 as assembled.Note that some structure (e.g., electrical and fluid lines, fasteners,etc.) may be removed from this and other views to more clearly describedaspects of the depicted embodiments. As shown in this view, the impeller431 of the blower 430, whose speed is controlled by the motor 433 undercontrol of the controller 437 on the PCB 434, may draw ambient gas intothe housing 403 via the passages 416, compress the gas, and provide theflow of pressurized gas at the outlet 432 of the blower 430.

As will be further described below, the humidifier 600 may include a CFV602 that vaporizes water 435 drawn from the reservoir 406 and emits thevapor into a humidification chamber 456 formed by the humidifier housing446. In some embodiments, a sensor, e.g., a temperature and humiditysensor 458, may be provided. While the sensor 458 may be located mostanywhere, it is, in one embodiment, located in the humidificationchamber 456. The sensor 458 may provide a signal representative of thetemperature and/or humidity level of ambient air at system startup. Byproviding the sensor 458 within the humidification chamber 456, thesensor may be used to monitor temperature and humidity during operationas well.

FIG. 13 is an exploded view of the exemplary humidifier 600. As shown inthis view, the humidifier 600 may include a vaporizing device that, inone embodiment, is a CFV 602 similar to that already described herein.The CFV 602 may include a vaporizing element 604, which may beconstructed of a sintered material, and a heating/ejection layer 606defining an outlet or opening 608. A water conveying device 610, whichmay be configured as a small diameter tube or as a wicking material, mayconvey water 435 from the reservoir 406 (see FIG. 12) to the vaporizingelement 604 via capillary action.

The humidifier 600 may further include a mounting sleeve 612 to hold theCFV 602. In one embodiment, the mounting sleeve 612 includes a groove614 to hold a seal (e.g., O-ring 616), the latter adapted to seal themounting sleeve relative to the humidifier housing 446/housing 403.

The mounting sleeve 612 may further include a receiver 618 for receivingand securing a PCB 620. Two contact members 622 may electrically couplecontacts on the PCB to electrical leads 624 on the heating/ejectionlayer 606 of the CFV 602 when the humidifier 600 is fully assembled. Alower cap 626 may attach (e.g., via a screw thread) to the mountingsleeve 612. The lower cap 626 may protect elements of the humidifier600, while also securing the water conveying device 610 within thehumidifier. When correctly installed, the humidifier 600 may makeelectrical connection with the housing 403 (e.g., with the humiditycontroller 630 on the PCB 434) via an electrical connector 628 of thehousing that engages associated contacts on the PCB 620.

FIG. 14 illustrates one embodiment of the humidifier 600 during use in aPAP housing, e.g., the housing 403. The humidity controller 630 maycontrol delivery of electrical power from a DC power supply 423 (seeFIG. 14, which could be a battery, or a DC transformer connected to anAC outlet). The humidity controller 630 may be in communication with thePAP controller 437 such that the water vapor output of the humidifier600 may be correlated with the flow of pressurized gas delivered by theblower 430.

To generate vapor output, the humidity controller 630 may command acurrent to pass to the electrical leads 624 (see FIG. 13). This currentcauses a rapid increase in heat of the vaporizing element 604 and theheating/ejection layer 606. As these layers heat, water vapor 632 isproduced and ejected through the opening 608 into the humidificationchamber 456 (see also FIG. 12). Water vapor, as used herein, may includeone or more of water vapor, liquid water droplets, mist, microdroplets,fog, and combinations of liquid water and water vapor.

As the vaporizing device vaporizes the water 435, more water istransferred to the vaporizing element 604 (as indicated by arrows 429 inFIG. 14) via the water conveying device 610 via wicking or capillaryaction. Of course, in other embodiments, a pump could be used to providewater to the vaporizing element 604. Thus, vaporization may continue aslong as the water level of the reservoir 406 is of a level that ensurescontact between the water conveying device 610 and the water. Thehousing 403, e.g., the PCB 620, could include a water level sensor 621that would trigger an alarm and/or shut off the humidifier 600 when thewater level was at or approaching empty. Moreover, some CFVconstructions may operate most effectively with distilled water. As aresult, some embodiments may include a water quality sensor 623 todetect impurities in the reservoir and respond, e.g., trigger an alarm,if threshold levels of impurities are detected.

Both the water level sensor 621 and the water quality sensor 623 may beelectrically connected to the humidity controller 630 or flow controller437, so that appropriate action may be taken in response to unacceptablewater level and/or water quality. In some embodiments, both the waterlevel detector 621 and the water quality detector 623 may utilize thesame sensor (e.g., sensor contacts 621). For instance, water level andwater quality may be assessed by monitoring the impedance between twoexposed contacts 621 formed on the PCB 620. An intermittent current orvoltage may be passed across the contacts (e.g., a 10 kHz symmetricalsquare wave), wherein a measured current or voltage may be detected whenthe contacts 621 are submerged. When water level drops below thecontacts 621, continuity between the contacts breaks, indicating to thecontroller 630 (or 437) an out-of-water condition. In such an instance,the controller may sound an alarm or terminate power to the humidifier.

In addition to water level detection, the contacts 621 may alsodistinguish whether the water in the reservoir is distilled or whetherit contains minerals that may potentially damage the CFV. For example,since distilled water has a very high but measureable impedance, and tapwater has ions and/or minerals that provide a lower impedance, thecontroller 630 (or controller 437) may distinguish between distilledwater and potentially damaging mineralized water. Based upon thedetermination that the water is not distilled, the controller 630 (or437) may sound an alarm, provide an alert message on the display 414(see FIG. 7), or even shut down the humidifier.

The water level sensor 621 and water quality sensor 623 may bepositioned in locations other than those shown in the figures. Forexample, the sensors could be in contact with the water in the waterconveying device 610 or at some other location within the reservoir 406.Moreover, other methods for detecting water level and quality may beutilized. For instance, piezo-electric sensors could be used. Suchsensors may be located at positions similar to the sensors 621 and 623.Alternatively, water level and/or quality sensors may be configured asnon-contacting sensors located above the water in the reservoir 604. Forexample, the water level sensor could be an ultrasonic sensor that emitsan ultrasonic sound wave and measures transit time of pulses reflectedfrom the water surface.

During operation, the apparatus (e.g., apparatus 400) may, uponinitialization, determine a relative humidity level of the ambient air.This may be accomplished using the temperature and humidity sensor,e.g., sensor 458. The user may set a desired target humidity level,e.g., via interaction with the control interface 410. Based upon therelative humidity of the ambient air and its temperature and pressure,and upon the user-selected target humidity level of the flow ofpressurized gas, the apparatus (e.g., PAP controller 437 orhumidification controller 630) may determine how much water vapor shouldbe added (per unit volume of gas) by the humidifier 600.

For example, if the apparatus determines that the ambient relativehumidity is 40% and the ambient temperature is 23 degrees Celsius (°C.), the absolute humidity can be determined from known relationships(see, e.g., www.humidity-calculator.com) to be approximately 8.3milligrams of water/liter of gas (mg water/L gas) for a given pressure.If the user wishes to achieve a target relative humidity of 80%, thiswould require an absolute humidity at the same temperature of 16.5 mgwater/L gas. As a result, the apparatus (e.g., the controller 437 orcontroller 630) can determine that the humidifier 600 would need to addabout 8.2 mg water/liter gas to achieve the desired target humiditylevel.

In one embodiment, the relationship between relative humidity andabsolute humidity may be provided in a lookup table contained in memory(e.g., memory 438 of the PCB 434, see FIG. 11). In other embodiments,the relationship may be defined as shown in Equation 1 below:

AH=(0.0583*e ^((0.0548*T)))*RH  (Equation 1))

wherein AH is the absolute humidity in mg water/L gas; T is thetemperature in degrees Celsius (° C.); and RH is relative humidity attemperature T expressed as a percentage. Based upon this equation, theapparatus 400 (e.g., the humidity controller 600 and/or the PAPcontroller 437) may calculate the vapor content need to achieve thetarget humidity level. As is evident from Equation 1 above, therelationship between AH and RH, for a given temperature, may beexpressed linearly.

Accordingly, apparatus in accordance with embodiments as describedherein (e.g., apparatus 70, 100, and 400) may calculate how much watervapor needs to be added per unit volume of gas flow to achieve thedesired target humidity level. As stated above, the apparatus maysubtract from these calculated humidity levels the moisture contentalready present in the ambient gas and provide only the difference asadded humidity to the flow of pressurized gas.

The apparatus (e.g., apparatus 70, 100, 400) may provide, at any giventime during operation, a signal representative of a rate of flow of thepressurized gas. Such a flow rate may be directly measured, e.g., with apneumotachometer (see pneumotachometer 134 of apparatus 100 of FIG. 4),or indirectly estimated, e.g., by analyzing changes in: power drawn by;or speed of, the impeller motor (e.g., motor 433).

With this information, power to the CFV (e.g., 302, 602) may bemodulated to achieve the constant target humidity level regardless ofchanges in the rate of flow of the pressurized gas. As an example, insome embodiments, the CFV (e.g., 302, 602) may be based upon a modelMyPUREMIST CFV 100 personal humidification unit. FIG. 15 illustrates anexemplary power versus water vaporization performance curve for thisparticular CFV model. As shown, the CFV may vaporize water in linearproportion to the amount of power provided to the CFV. As a result, thecontroller (e.g., humidity controller 630) may command the CFV toprovide only that amount of humidity needed at any given time byaltering the level of electrical power provided to the CFV. Theillustrated relationship between power provided to the CFV and theamount of water vaporized (in cubic centimeters/minute (cc/min)) for theCFV may be expressed as:

P=(45.3*F)+0.6  (Equation 2)

Wherein P is the power in watts provided to the CFV and F is thevolumetric flow of water vaporized (in cc/min). The actual powercalculated by Equation 2 may include a power efficiency loss factor thatmay be added as a multiplier (linear or nonlinear), or as an offsetfactor, to accommodate performance characteristics of any particular CFVor system construction.

Accordingly, in its simplest implementation, apparatus as describedherein (e.g., apparatus 70, 100, and 400) may, based upon theinstantaneous rate of flow of the pressurized gas detected in thesystem, energize and modulate the humidifier (e.g., 73, 300, 600) toprovide the target humidity level to the user in a continuous modulationhumidification mode.

While the vapor produced by the CFV may be proportional to theelectrical power provided to the vaporizing device, such a configurationis not limiting. Rather, in other embodiments, most any transferfunction, or combination of transfer functions, could define therelationship between electrical power to the CFV and the resulting watervaporized based upon a given CFV design and based upon an apparatus inwhich the CFV is used. Using the CFV from the model MyPUREMIST CFV 100,power losses may be present and the slope of the curve in Equation 2 mayincrease with a partial multiplier of this equation.

FIG. 16 is a flow chart illustrating a generalized, exemplary method ofoperating a PAP apparatus (e.g., apparatus 70, 100, or 400) in thecontinuous modulation humidification mode. The apparatus may be poweredon at 634. During an initialization period, the humidifier (e.g., CFV602 of the humidifier 600) may remain unpowered so that the apparatusmay determine ambient conditions of the gas including humidity level andtemperature while the blower is producing the predetermined pressure(e.g., the pressure previously set by the overseeing clinician) at 636.These parameters may be determined via measurement using sensors (e.g.,the temperature and humidity sensor 458 (FIG. 12) and relayed to the PAPcontroller 437 and/or the humidification controller 630. In someembodiments, the pressure could also be measured at this time. In otherembodiments, the user may input the approximate temperature and humidityusing the joystick 412 and screen 414.

During or before the initialization period, the user may select adesired target humidity level (e.g., using the control interface 410).The apparatus may then compare vapor content of the ambient gas to thetarget humidity level at 638 and then calculate the difference as theamount of vapor to be added to the flow of pressurized gas at 640. Oncethis is determined, the controller (e.g., humidification controller 630)may begin modulating power to the humidifier (e.g., to the CFV) tocorrespondingly modulate humidity added to the flow of pressurized gasin proportion to the rate of flow of the pressurized gas at 642. Therate of flow of the pressurized gas may be provided, in one embodiment,to the humidification controller 630 by the PAP controller (e.g.,controller 437). This operation may continue unless a system fault orsystem termination is detected at 643, at which point the apparatus mayinitiate a humidifier shutdown sequence at 644.

As stated above, while the continuous modulation humidification mode iseffective, humidity of a particular level is of benefit to the userprimarily during inspiratory portions of the user's breathing cycles.That is, maintaining a desired target humidity level at the userinterface may provide little benefit to the user during expiration. As aresult, if the humidity added to the flow of pressurized gas reachingthe user interface during expiration were reduced or terminated (e.g.,added humidity from the CFV were discontinuous or pulsed), water andpower conservation may be realized without negatively impacting theuser.

The CFV is positioned remotely from the user interface in the exemplaryPAP apparatus 70, 100, and 400. As a result, in order to provide thetarget humidity level to the user primarily when the user is inspiringrequires the PAP apparatus to predict when the added humidity should beinjected into the flow of pressurized gas to account for the delaybetween adding the humidity to the flow of pressurized gas and the flowof pressurized gas with the added humidity reaching the user interface.FIG. 17 illustrates an exemplary method of providing added humidity insuch a discontinuous humidification mode.

In general, the process illustrated in FIG. 17 includes steps 634, 636,638, and 640 already described above with reference to FIG. 16. However,after step 640, the process of FIG. 17 proceeds to step 645. At 645, thecontroller (e.g., controller 437 or 630) may automatically determine orpredict when the onset of the inspiratory phase of the next breath cyclewill occur and determine/predict a duration of that inspiratory phase at645. This prediction may, in one embodiment, be based upon analyzing thecurrent breath cycle or one or more prior or previous breath cycles andanticipating that the next breath cycle will be similar.

Based upon this prediction, the controller (e.g., controller 437 or 630)may automatically select or calculate a power interval start time ordelay (e.g., a period of time measured from an indexing event afterwhich power will be provided to the CFV) and power interval duration at647. “Power interval” or “power interval duration” as used herein refersto the time period in which the controller (e.g., humidificationcontroller) provides electrical power to the humidifier (e.g., to theCFV) at a level that causes the CFV to add humidity (as water vapor) tothe flow of pressurized gas. The power interval start time (based uponthe power interval delay) and power interval duration are selected orcalculated in an attempt to ensure that the flow of pressurized gas withadded humidity 140 (see, e.g., FIG. 6) reaches the user interfacebeginning at or near the onset of the respective inspiratory phases andlasts for most or all of the inspiratory phases (e.g., expires at ornear the end or onset of each respective expiratory phase). Once again,the humidification controller may modulate power to the CFV during thepower intervals to maintain the target humidity level within the flow ofpressurized gas with added humidity even as the rate of the flow ofpressurized gas changes. The humidification controller may select orcalculate, based upon the time remaining until expected inspiration, thestart time and duration of the power interval that will result in: addedhumidity (at the target humidity level) being provided to the flow ofpressurized gas that reaches the mask during inspiration; and a lesserlevel of humidity (or no added humidity) reaching the mask duringexpiration (i.e., each flow of pressurized gas with added humidity atthe user interface may end at or near the onset of the expiratory phaseof its respective breath cycle).

In some embodiments, the power interval delay time is triggered from astart of inspiration. That is, the controller (e.g., controller 437 or630) may detect when the inspiratory phase of a preceding first breathcycle begins and then initiate the power interval delay and duration forthe subsequent target breath cycle based thereon. While described asindexed from the start of inspiration, the power interval delay timecould be based upon most any event trigger that occurs during eachbreath cycle (e.g., start of expiration, peak expiratory or peakinspiratory flow).

After the specified power interval delay elapses at 649, power to theCFV may be initiated (e.g., the power interval may start) and modulatedin proportion to the flow of pressurized gas at 651 to achieve thetarget humidity level. This may continue until the power intervalexpires at 653, at which point control is passed to 655. At 655, powerto the CFV is: reduced to a point where little or no vapor is added tothe flow of pressurized gas; or terminated altogether. The process maythen determine whether treatment is complete or the PAP apparatus hasencountered a fault (e.g., low water reservoir level, CFV fault, lowbattery (where used) power remaining, etc.) at 657. If not, control mayreturn to 645. Otherwise, a shutdown sequence may be initiated at 659.The shutdown sequence may disable power to the humidifier (e.g.,humidifier 600) and may take other steps, e.g., provide a visual oraudible alarm.

While these methodologies describe generally how a PAP apparatus mayprovide continuous or discontinuous humidification modes, the followingexamples describe more specific implementations.

Examples

In one example, a computer model was built to simulate different PAPbreathing scenarios. For each of these PAP breathing scenarios,humidifier power interval delay (e.g., indexed from a start ofinspiration) and power interval duration (e.g., for discontinuoushumidification) were then iteratively input into the computer model andthe results analyzed. Based upon this analysis, specific values forpower interval delay and duration were selected (for each scenario) thatyielded the desired target humidity level at the user interface duringthe inspiratory portion of each breath cycle, and reduced or terminatedadded humidity to the user interface during the expiratory phase of eachbreath cycle.

A substantial number of breathing scenarios that might be encounteredduring typical PAP operation were investigated using the computer modelsimulation, and corresponding values for power interval delay andduration were iteratively determined for each scenario. These values,could, in one embodiment, be stored, e.g., as a lookup table, within (orotherwise accessible by) the PAP apparatus (e.g., apparatus 70, 100, and400). Based upon actual sensor measurements and system inputs (e.g.,flow, pressure, etc.), the PAP apparatus could then identify thesimulation scenario within the lookup table that most closely matchesthe actual breath cycle and then select the power interval delay andduration values associated with that lookup table entry. Of course, sucha system could constantly update the set of parameters being used (andtherefore update the power interval delay and duration) to closelyfollow the user's instantaneous breath cycle.

The exemplary computer model allows for manual input of pertinent systemand breath parameters including: hose volume (e.g., hose length anddiameter); user interface (mask dead space) volume; intentional leak;PAP pressure; user breath rate; I/E ratio; tidal volume; inspiratory andexpiratory flow dynamics/patterns; unintentional leak; ambient humidityand temperature; and target humidity and temperature, among others. Withthese parameters fixed each scenario, values for power interval delayand duration were manually iterated until the most appropriatehumidification values were determined.

With reference to FIG. 18, the exemplary computer model may firstprovide a process for calculating flow dynamics for a particularbreathing scenario. For purposes of this discussion, the PAP apparatusmay be similar to the apparatus 100 shown in FIGS. 4 and 6. “Flowdynamics” refers to the characteristics (e.g., shape amplitude, breathrate, etc.) of the flow versus time curve.

The process starts at 701. Initial parameters regarding the PAPapparatus may first be provided. For example, hose (e.g., hose 106)information may be input at 702. Hose information may be input as alength and diameter, or directly as a hose volume. Of course, whenimplemented on an actual PAP apparatus, the hose information could beinput into the PAP apparatus as a part number or other hose identifier,from which the PAP apparatus could, e.g., via a lookup table, determinethe actual hose volume. Similarly, information regarding the mask (e.g.,mask dead space) may be input at 704. Once again, the mask dead spacemay be provided directly to the PAP apparatus, or the apparatus coulddetermine (e.g., via a lookup table) the dead space based upon a maskpart number or other inputted identifier.

The PAP pressure (which is typically determined and set by a clinician)may be input into the model at 706. Based upon the intentional mask leak(which may be part of the mask information inputted at 704), thesimulation may determine an appropriate equation or lookup table formask leak flow versus pressure at 708, and the mask leak flow (Fm) maybe calculated at 710.

The model may further have as inputs: an estimated unintentional maskleak flow (Fu) at 712; a breath rate at 714; an inspiratory:expiratory(I:E) ratio at 716; and a tidal volume (Vt) at 718.

The model may also permit the input or selection of one or morebreathing types at 720. For example, a sinusoidal breathing pattern maybe selected, as well as other predefined shapes. Based upon thebreathing type selected for the simulation, an equation may bedetermined (e.g., selected from a lookup table or otherwise calculated)that represents lung flow (Fl) versus time at 722.

A desired sampling time increment (dt) may be input at 724, and for time(t) set equal to zero, lung flow (Fl) and lung volume (Vl) may be set tozero at 726. Moreover, hose flow (Fh) may be calculated (at time zero)to be equal to the sum of Fl, Fm, and Fu at 728.

The simulation may increment time by dt at 730 and then re-calculatelung flow Fl (at 732), lung volume Vl (at 734), and hose flow Fh (at736). Assuming that a time period for the simulation has not expired at738, control will return to 730 as shown and the calculations at 732,734, and 736 will repeat for each time increment. Once the simulationtime period (e.g., a period equal to several breath cycles) has expiredat 738, the computer model may end the simulation at 740. The simulationmay store the values for lung flow Fl (at 732), lung volume Vl (at 734),and hose flow Fh (at 736) for each time increment dt, along withcalculations of: the timing of humidification delivered to the airwayrelative to the breathing cycle; the power delivered at each time step;and the average power and water consumed over each inspiratory phase,expiratory phase, and complete breathing cycle. By varying the inputsinto the computer model and repeating this process, simulation modelsfor dozens, hundreds, or even thousands (or more) of permutations ofbreathing and system variables (the scenarios) may thus be developed.

Based upon each breath simulation generated, humidification parameterswere then evaluated (while the remaining variables for the simulationremain fixed). As shown in FIG. 19, such an exemplary process may beentered at 801. The computer model may receive, as inputs, variousparameters regarding the actual humidifier, e.g., CFV 302 (or 602). Inthese examples, the humidifier is again the CFV device from a modelMyPUREMIST CFV 100. Accordingly, the humidifier parameters entered at802 may include the power-to-water vaporization equation (see, e.g.,Equation 2 above). Other parameters of the CFV, e.g., vaporizationinitiation delay (e.g., a delay between power delivered to the CFV andemission of vapor) and a vaporization termination delay (e.g., a delaybetween power termination to the CFV and termination of emission ofvapor) may also be input at 802.

The ambient relative humidity (RHa) and ambient temperature (Ta) may beinput at 804. With this information, the ambient absolute humidity (AHa)may be calculated (see, e.g., Equation 1 above) at 806. The targetrelative humidity (RHt) may be input at 808, and the target absolutehumidity (AHt) calculated at 810. The difference between the target andambient absolute humidity (AHt−AHa) may be calculated at 812 to yieldthe additional vapor to be provided by the humidifier/CFV.

The computer model may be configured to simulate either continuous(e.g., continuous modulation mode) or discontinuous (e.g., discontinuousmode) humidification. For continuous humidification, a power intervaldelay time (Pdt) may be set to zero at 814, and a power intervalduration time (Pdu) may be set to continuous at 816. On the other hand,for discontinuous humidification, a first iterative value for Pdt (e.g.,which may be triggered by the onset of inspiration) may be input at 814,while a first iterative value for Pdu may be input at 816. Once again,as will be evident below, the values of Pdt and Pdu can be iterativelyrevised and the respective simulation re-run for each identifiedbreathing scenario.

In addition to the power interval parameters, the type of powermodulation (transfer function) that will be used (e.g., proportionalflow modulation, step function input (e.g., square wave), orcombinations thereof) may be input at 818.

The supply voltage available to the humidifier may be input or otherwisedetermined at 820, while the minimum input power level that will beprovided to the CFV during operation (e.g. which may be zero watts orsomething higher) and the maximum input power level to the CFV may beinput at 822 and 824, respectively.

The computer model may also receive the following inputs: tidal volume(Tv) at 826; I:E ratio at 828; system pressure (P) at 830; breath rate(e.g., breaths/minute) at 832; and the time interval step (dt) desiredat 834. The simulation/system time (t) may then be set to zero at 836(some of these parameters may have been input earlier, see, e.g.,process of FIG. 18).

Control is then routed from 836 to 838. If continuous humidification isselected, the model first determines or detects lung flow Fl and hoseflow Fh at 840 (see 732 and 736 in FIG. 18). The model may thencalculate a current cumulative hose volume (Vcch) at 842. Vcch, as usedherein, is the cumulative volume of gas that the PAP has outputted as ofthe current time (e.g., may be calculated by integrating hose volume Flover the elapsed time). The model may then calculate, at 844, theelectrical power needed to be supplied to the CFV in order to reach thetarget ambient humidity level AHt. This electrical power can then beapplied to the humidifier (e.g., to the heater of the CFV) based uponthe instantaneous hose flow Fh at 846. The computer model may then savethe values for time (t) and for the current cumulative hose volume(Vcch) for each time step in which electrical power to the humidifier isbeing modulated at 848.

Next, the computer model may calculate the cumulative hose volume Vch at850. As used herein, the cumulative hose volume (Vch) is calculated bysubtracting from the current cumulative hose volume (Vcch) the sum of:the hose volume (as measured from the outlet 318 of the humidifier); andthe mask volume. For instance, in the system shown in FIG. 4, thissubtracted sum would include the volume of the flow path measured fromthe outlet 318 of the CFV to the face seal of the mask 108. Accordingly,Vch will be less than Vcch at any given time.

The computer model may then, via a lookup table (or calculation),determine a time entry (tx) associated with the calculated value of Vchat 852. If the time entry tx in the lookup table that is associated withVch specifies that power to the humidifier is on at 854, then the time tand current cumulative hose volume Vcch are tagged as providing humidityto the mask at 856.

If the answer at 854 is no, then the computer model may check to see ifthe end of the expiratory phase of the current breath cycle has occurredat 858. If not, the time t may be incremented (e.g., by dt) at 860 andcontrol returned to 840 as shown. If, on the other hand, the end ofexpiration has occurred, then the model may calculate the peak andaverage power provided to the humidifier over the just-ended breathcycle at 862, as well as the peak and average power utilized over allthe previous breath cycles at 864. Of course, given the knownrelationship between water vapor added by—and power provided to—thehumidifier, the average vapor added to the flow of pressurized gas mayalso be determined. These values may be stored for subsequentutilization.

The computer model may continue by incrementing time by dt at 868 andreturning to 840 until an adequate time period (e.g., at least as greatas several breath cycles) has expired at 866, in which case the modelmay end at 870.

If discontinuous humidification is selected (e.g., at 814 and 816 ofFIG. 18), then control is passed from 838 in FIGS. 19 to 901 in FIG. 20.A breath cycle counter may set the breath cycle count (B) equal to n(e.g., zero) at 902. After incrementing time by dt at 904, lung flow Fland hose flow Fh may be determined or otherwise detected at 906. Lungflow Fl may be expressed as a function of breath rate and tidal volume,while hose flow Fl may be expressed as the sum of lung flow and ventflow (the latter which may be expressed as a function of systempressure).

Current cumulative hose volume (Vcch) may be calculated at 908. In someembodiments, Vcch may be calculated by integrating hose flow Fh over thetime elapsed. Once again, the model may determine or detect (based uponthe flow dynamics) when the inspiratory phase begins at 910. Ifinspiration is detected at 910, then the time t is tagged as the startof inspiration at 912. The peak and average power used over thejust-completed breath cycle, as well as the peak and average power usedover all previous breath cycles, may then be calculated at 914 and 916,respectively. The start of inspiration may also result in indexing thebreath cycle counter to the next breath cycle (e.g., n+1) as indicatedat 918. If the start of inspiration is not detected at 910, then controlpasses to 920, where the time t is tagged as being within the currentbreath cycle.

From both 918 and 920, control is passed to 922 to determine the timethat has elapsed (te) since the start of inspiration of the currentbreath cycle was detected at 910. This elapsed time te may be calculatedbased upon the current time t and the breath rate.

The computer model may then, at 924, determine whether the elapsed timete determined at 922 satisfies two humidifier power conditions: (1) iste greater than or equal to the power interval delay (Pdt; inputted at814); and (2) is te less than or equal to the sum of the power intervaldelay (Pdt) and the power interval duration (Pdu; inputted at 816). Ifso, it is known that the humidifier power is on and control passes to926. Otherwise, control may pass to 928.

At 926, the computer model may calculate the electrical power needed toprovide the flow of pressurized gas with the target ambient humidity(AHt). Based upon the power-to-water vaporization equation and the hoseflow Fh (see, e.g., Equation 2), the power to the heating element of thehumidifier may then be modulated (e.g., in accordance with themodulation type input at 818) at 930.

The values for time t and current cumulative hose volume Vcch (thelatter calculated at 908) may then be saved and marked as beingassociated with power modulation of the humidifier at 934, after whichcontrol may pass to 928. At 928, the cumulative hose volume Vch may becalculated by, as stated above, subtracting from the current cumulativehose volume (Vcch) the sum of: the hose volume (as measured from theoutlet 318 of the humidifier); and the mask volume.

Once Vch is determined, a time entry tx (e.g., from a lookup table orcalculation) that corresponds to that value of Vch (or the next largestvalue of Vch) is determined at 932. The lookup table can then determine,for this time entry tx value, whether the humidifier power is on or offat 936. If the answer at 936 is yes, then the time t and Vcch are markedas occurring while humidity is provided to the mask at 938. In eitherevent, control is passed to 940. If the simulation time period hasexpired, the process may then end at 942. Otherwise, control may returnto 904 as shown.

As indicated above, in the illustrated examples, the power intervaldelay time is indexed from the beginning of the inspiratory phase ofeach breath cycle (the “indexing event”). However, such a configurationis not limiting. For instance, peak inspiratory flow, inspiratory lungvolume, peak expiratory flow, and expiratory lung volume, among others,could each be used as the indexing event.

Once again, for any given set of breathing and physical conditions(i.e., for any one of the scenarios modelled), multiple simulations wererun that iteratively covered a range of humidifier conditions (e.g., arange of power interval delays and power interval durations) while allother variables remain constant. These iterations were then evaluated toidentify the values of Pdt and Pdu that provided the desired targethumidity level at the user interface during most or all of eachinspiratory phase of each scenario, but provided less or no addedhumidity to the flow of pressurized gas at the user interface duringeach expiratory phase. Once the best solution to each scenario wasdetermined, a lookup table of power interval delay and power intervalduration times was constructed and indexed to the respective scenarios.Such a lookup table may be similar to that shown in Table I. below,wherein for each scenario, Pdt and Pdu are tabulated.

TABLE I Power Interval Delay, Power Interval Duration, BreathingScenario seconds seconds 1 Pdt(1) Pdu(1) 2 Pdt(2) Pdu(2) 3 Pdt(3) Pdu(3)n Pdt(n) Pdu(n)

In evaluating the iterative results to create each record in the lookuptable, various characteristics of the simulations may be analyzed. Theseinclude, among others: how much humidity is delivered to the userinterface during inspiration; what is the duration of the humiditydelivered relative to the duration of the inspiratory phase; how muchadded humidity is provided at the user interface during expiration; andwhat is the relative humidity at the user interface compared to thetarget relative humidity. As discovered, a solution may exist for manybreathing scenarios that provides the desired target humidity duringinspiration, while reducing or terminating added humidity duringexpiration.

The lookup table (e.g., Table I) could be incorporated into an actualPAP apparatus (e.g., 70, 100, or 400). The PAP apparatus (e.g., itscontroller(s)) could then continuously monitor parameters such as lungflow and hose flow (among others) and compare them to the breathingscenarios contained in the lookup table to determine which table entryis most appropriately matched to the current (e.g., measured) flowpattern. Once found, the appropriate power interval delay and durationvalues Pdt and Pdu from that table entry could be used to control theCFV and provide the desired humidification. Of course, the controller(s)may update these parameters in real time, e.g., every calculation cycle,to ensure that the most accurate humidification parameters are beingused throughout the treatment period.

In other embodiments, the simulation (or the PAP and/or humidificationcontroller) may include the capability to automatically predict anappropriate power interval delay and power interval duration for a givenbreathing scenario without requiring the manual iterations describedabove. For example, the simulation (or controller) may accept any of theinput or determined parameters described above with respect to FIGS.18-20. However, instead of inputting specific breathing characteristicsand flow dynamics, the system (e.g., PAP apparatus) may measure theseparameters during each breath cycle and then, based upon calculationsusing those parameters, predict a power interval delay (Pdt) and powerinterval duration (Pdu) for the now-current or next breath cycle thatachieves the desired humidification goal. Once again, such a simulationmodel could be programmed directly into the PAP and/or humidificationcontrollers to calculate directly the power interval delay and durationwithout the need for lookup table entry matching. Of course, thecontroller(s) could again update these parameters in real time, e.g.,every calculation cycle, to ensure that the most accurate humidificationparameters are being used throughout the treatment period.

One embodiment that utilizes a predicted/calculated power interval delayand duration is illustrated generally in FIG. 21. As shown in this view,the end of the expiratory phase of a breath cycle “n” (e.g., whichcorresponds with the beginning of a subsequent breath cycle “n+1”) maybe detected at 1002 based upon any number of methods. The simulation maythen measure/analyze characteristics of the previous breath cycle n at1004. For example, the characteristics analyzed may include breath rate,I:E ratio, breath waveform, flow, volume, pressure, and/or otherbreathing parameters.

Based upon an analysis of these characteristics of the breath cycle n,ideal values for power interval delay (Pdt) and power interval duration(Pdu) that would have provided effective humidification (e.g., providedpower to the CFV in a way that would have produced the desired humiditylevel at the mask for most or all of the inspiratory phase whileproviding little or no additional humidity at the mask during theexpiratory phase) during the breath cycle n may be calculated at 1006.

These ideal values of Pdt and Pdu calculated at 1006 may then becompared, in one embodiment, to the actual values of Pdt and Pdu thatwere used during the breath cycle n, and a difference or errorcalculated at 1008. In some embodiments, similar error calculations maybe made comparing the ideal values of Pdt and Pdu calculated at 1006 toaverage values of Pdt and Pdu for two or more previous breaths. In yetother embodiments, error calculations may be generated based upon: theprevious breath, the previous two breaths, and on up to the previous xbreaths (where x is greater than or equal to three).

If it is found at 1010 that one or more of the errors calculated at 1008exceeds a threshold value, control may pass to 1012, wherein acontinuous modulation humidification mode is activated, after which thebreath count B is indexed at 1016, and control returns to 1002. Thecontinuous modulation humidification mode may remain active untilbreathing has stabilized, which may be determined by the errorscalculated at 1008 dropping below the threshold values at 1010. Thethreshold value of error may be based upon some predetermined criteriathat suggests breathing has become too erratic to permit accurateprediction of Pdt and Pdu.

If, on the other hand, the error determination at 1010 is below theestablished threshold error level, control may pass to 1014. Based uponthe error calculations made at 1008, values of Pdt and Pdu may beselected/predicted for the next (now-current) breath cycle (n+1) at1014. For instance, the values of Pdt and Pdu for the next breath cyclemay be based upon the lowest error calculated at 1008. Alternatively,the various errors calculated at 1008 may be averaged and used topredict Pdt and Pdu for the next breath cycle.

After selecting Pdt and Pdu, the breath cycle counter may be indexed toreflect the actual breath cycle count at 1016, after which control isreturned to 1002.

Thus, in some embodiments, the simulation (or the PAP or humidificationcontroller) may at the end of each breath cycle, calculate an optimal orideal power interval delay and power interval duration for thatjust-completed breath cycle and compare those values to the predictedvalues that were actually used during the just-completed breath cycle(and/or to one or more other preceding breath cycles) to generate one ormore errors for both Pdt and Pdu. In the event that one or more of thosecalculated errors exceeds a threshold, the process may resort tocontinuous power modulation (continuous modulation humidification mode)until the calculated error(s) returns to acceptable levels.

Error calculation (see, e.g., 1008 in FIG. 21) may be based upon one ormore levels of testing. For instance, the values of Pdt and Pdu may becompared to the corresponding values of the immediately precedingbreath, and/or on the corresponding values from two or more previousbreaths. In the case of the latter, the errors from the two or moreprevious breaths may be analyzed and the lower error values used topredict the power interval delay and duration for the next breath.

While described as a simple average, other embodiments may calculateerror based upon a more sophisticated statistical analysis. Forinstance, other embodiments may calculate error based upon weighted ormoving averages, standard deviations, trend analyses, etc. where suchanalyses are beneficial to the accurate prediction of Pdt and Pdu.

As the process of FIG. 21 demonstrates, operation may default toproviding the desired humidity level via the continuous modulationhumidification mode when the PAP system (e.g., controller(s)) is unableto accurately predict Pdt and Pdu by setting Pdt to zero and Pdu tocontinuous duration. Such a feature may be advantageous for many usersand situations, e.g., those who experience numerous periods of unstablebreathing over the course of the treatment period, those transitioningbetween sleep stages, and those changing body positions.

In addition to predicting Pdt and Pdu based upon an analysis of one ormore previous breaths, systems/methods like those described above andshown in FIG. 21 may, at any time during a breath cycle, if anybreathing parameter is found not to be following the expected course,utilize current, real-time measurements to recalculate the powerinterval delay and duration instead of waiting until the end of eachexpiration. In this way, the simulation model (or actual PAPmeasurements) may function as a test of prediction accuracy, wherein thesystem may ultimately fallback to continuous modulation humidificationmode in the event that prediction accuracy deviates from a predeterminedthreshold.

Breathing scenarios using predicative humidification concepts andreal-time, controller-calculated values for power interval delay andduration (as described above with reference to FIG. 21) are shown inFIGS. 22A-22C for certain situations having stable breathing patterns.FIGS. 22A-22C illustrate computer-generated simulations of variousbreathing scenarios and how such scenarios may be accommodated by PAPand humidification systems and methods in accordance with embodimentslike those described herein. As evident from these figures, PAP systemsand methods may, based upon an analysis of various breathing parameters,predict when to provide power to the CFV (e.g., determine the powerinterval delay time) and when to de-energize or substantially reduceelectrical power to the CFV (e.g., the power interval duration), as wellas how to modulate the electrical power to the CFV during operation. Asa result, providing a flow of pressurized gas having a generallyconstant level of humidity at the user interface 108 during inspiration(regardless of gas flow rate), and reducing or even terminating theadded humidity to the flow of pressurized gas at the user interfaceduring expiration, may be achieved for many typical PAP breathingscenarios.

The simulations of FIGS. 22A-22C are based upon a system configured asshown generally in FIGS. 4 and 6, and are for a constant pressure PAP(CPAP) apparatus. Each simulation assumes: the distance 320 (see FIG. 6)between the CFV 302 and the user interface 108 is 72 inches (183centimeters) and that the delivery tube has an inner diameter of 21 mm;a hose volume of 633 cc; a mask dead space or volume of 100 cc; and anintentional leak of 4 mm (i.e., the vent 114 provides a port sizeequivalent to a hole of 4 mm in diameter).

Moreover, tidal volume is assumed to be 500 cubic centimeters (cc); theambient temp is 23 degrees C.; the ambient relative humidity is 40%; thetarget relative humidity is 90%; the I:E ratio is 1:1; and a powerefficiency factor of the CFV is 1.25. The simulations seek to deliveradded vapor to achieve the target humidity level during the entireinspiratory portion of each breath cycle. With these assumptions, FIG.22A illustrates a simulation at a PAP pressure of 20 centimeters (cm) ofwater and a breath rate of 10 breaths/minute (i.e., a breath period ofsix seconds); FIG. 22B is a simulation at a PAP pressure of 4 cm ofwater and a breath rate of 10/breaths/minute; and FIG. 22C is asimulation at a PAP pressure of 4 cm of water and a breath rate of 15breaths/minute (breath period of 4 seconds).

As already discussed above, the simulation model measured or calculatedseveral parameters (the “measured or calculated system parameters”).These measured or calculated system parameters may bemeasured/calculated based upon sampling at some time interval (e.g.,every 10-50 milliseconds). Any or all of these calculated parameters maybe continuously updated and stored for operational use or subsequentclinician interrogation. These measured or calculated system parametersmay include: total hose flow (e.g., intentional leak, unintentionalleak, and breath flow); breath rate; inspiratory tidal volume;expiratory volume; I:E ratio; inspiratory and expiratory flow dynamics(e.g., parameters representing the shape of inspiratory or expiratoryflow versus time); a start and an end of the inspiratory portion of eachbreath cycle; a start and an end of the expiratory portion of eachbreath cycle; the time of peak inspiratory flow; and the time and peakexpiratory flow. PAP pressure may also be included as measured orcalculated parameter.

A plot of an exemplary simulation model is illustrated in FIG. 22A. Asshown in this figure, a sinusoidal first curve 502 represents lung flow,while a sinusoidal second curve 504 represents total flow (e.g., hoseflow) in the delivery conduit 107 (lung flow plus intentional leakagethrough vent 114 (see FIG. 4) plus estimated unintentional leak flow).The first and second curves 502, 504 are generally identical, but offsetby the amount of the leak, which is about 32 liters/minute in thissimulation. A first, e.g., inspiratory, portion 506 of the lung flowcurve represents the inspiration phase of the breath cycle 510, while asecond, e.g., expiratory, portion 508 of the lung flow curve representsthe expiratory phase of the breath cycle. Of course, consecutiveportions 506 and 508 together define a single breath cycle 510 (thesuffixes “−1,” “−2,”, “−3,” etc. of reference numeral 510 representdistinct breath cycles, e.g., breath cycle 510-1 is an initial breathcycle, breath cycle 510-2 immediately follows breath cycle 510-1, breathcycle 510-3 immediately follows breath cycle 510-2, etc.).

As described earlier, the simulation model may be capable of determiningor calculating a variety of breath parameters. Based on variousmeasurements or inputs of tidal volume and pressure, the controller(e.g., controller 303 of FIG. 4) may calculate the power interval delay(Pdt) 512 to be applied beginning at the initiation of each inspiration.In the scenario shown in FIG. 22A, the power interval delay 512 is 3.85seconds. In general, the power interval delay 512 correlates an activityat the user interface 108 (e.g., inspiration) with an operation of theCFV 302 (e.g. vapor emission), the latter being located the distance 320upstream from the user interface 108. Stated another way, the powerinterval delay 512 may be calculated or selected, based on varioussystem parameters, to ensure that vapor is introduced into thoseportions of the flow of pressurized gas that will ultimately reach theuser interface 108 as the user begins to inhale. While shown as beingtriggered by the beginning of an inspiratory phase of a breath cycle,this trigger (initialization of the power interval delay) could be basedupon other breath parameters as indicated herein.

Moreover, the computer model may simulate the application of power (see,e.g., CFV power curve 516, further described below) to the CFV 302 for apower interval duration or period 514 (Pdu) as illustrated in FIG. 22A.The power interval duration 514 may be selected to ensure that the flowof pressurized gas with added humidity delivered at the user interfaceat the beginning of inspiration continues for most or all of theinspiratory phase 506 of each breath cycle 510, yet is reduced orsuspended during the expiratory phase 508. In the embodiment illustratedin FIG. 22A, the power interval duration is 4.05 seconds. In FIG. 22A,the sections 518 of the inspiratory phases of the breath cycles 510-2and 510-3 (curve 502) indicates when the humidity added by the CFVreaches the user interface based upon the model simulation. As shown inthis view, by delivering power to the CFV in accordance with the powercurve 516, the added humidity reaches the user interface for most of theinspiratory portion of each breath cycle, while little or no addedhumidity reaches the user interface during the expiratory phase.

In addition to turning power to the CFV 302 on and off (or at leastreduced to a minimum threshold power), simulated power to the CFV may bemodulated during use as represented by the power curve 516 in FIG. 22A.That is, power to the CFV 302 may be modulated in proportion to the flowrate of the gas in the system such that vapor content of the humidifiedgas remains relatively constant even as the flow of pressurized gasmoving past the CFV 302 changes. For example, in FIG. 22A, the power tothe CFV 302 varies from about 9.7 watts (w) to about 27 w, during thepower interval. Moreover, in this simulation, for any given breathperiod, the CFV is inactive (e.g., unpowered) for about 1.95 seconds,yielding an average per breath cycle wattage utilized of about 12 w. Theactual humidity level attained may be dependent on many factors.However, in this case, 0.58 watts/liter of gas flow per minute isestimated to raise the relative humidity from 40% to 90% at an ambienttemperature of 23 degrees C., taking into account the CFV inefficienciesof the particular configuration. The actual wattage may vary based upon,for example, the efficiency of the CFV, the ambient temperature, and theheat energy lost from the CFV to the surrounding structure and air.

Results similar to that illustrated in FIGS. 22A-22C were observed usinga bench test apparatus similar in many respects to the apparatus 100 ofFIG. 4. The test apparatus included simulated breathing loads at themask, and included various sensors (e.g., at the mask 108) to confirmaccuracy of the various humidification prediction methods describedherein (e.g., wherein power interval delay and duration were determinediteratively or, as shown in FIGS. 22A-22C, were calculated automaticallyin real time by the controller).

FIG. 22B illustrates a scenario simulation plot similar to FIG. 22A(i.e., tidal volume (500 cc) and breath rate (10 breaths/minute) beingthe same), but with PAP pressure set to 4 cm of water. As shown in thisview, the power interval delay 512, power interval duration 514, andpower curve 516 (e.g., average power/cycle and maximum power/cycle) maychange as shown in Table II.

FIG. 22C illustrates a scenario simulation plot similar to FIG. 22B (PAPpressure is set to 4 cm of water, tidal volume is 500 cc), except thatthe simulated breath rate is at 15 breaths per minute (a breath periodof 4 seconds). Table II again shows the values determined/calculate forthis specific simulation.

TABLE II Power Power Interval Interval Average Peak Minimum Delay,Duration, power/ power/ power/ PAP Pressure, seconds seconds cycle,cycle, cycle, cm of water (512) (514) watts watts watts 20 (FIG. 22A)3.85 4.05 12.1 27.3 0 4 (FIG. 22B) 1.65 5.6 8.5 17.3 0 4 (FIG. 22C) 0.553.9 11.2 21.7 0

Accordingly, it can be seen from these computer simulations how anexemplary PAP apparatus 100 could accommodate a wide variety of systempressures while still providing the benefit of precise vapor deliverywith minimal power required. Moreover, as shown in FIGS. 22A-22B, as thesystem pressure drops (with other breathing parameters being equal), thepower interval delay and power may decrease, while the power intervalduration may increase. At one point, see, e.g., FIG. 22B, the powercurve 516 may drop to zero (e.g., at peak expiration). This couldindicate that simulated flow has actually reversed in the deliveryconduit 107.

While these simulations indicate that an exemplary PAP apparatus (e.g.,apparatus 100) may accommodate different breathing scenarios while stillproviding the desired vapor delivery, certain scenarios may presentissues. For example, the ability to deliver vapor to the user during theentire inspiratory phase of each breath cycle could be adverselyaffected by: low breath rates; high leaks (intentional andunintentional); and low PAP pressures. For example, in the simulation ofFIG. 22C, humidified gas (portions 518 of inspiratory phase 506) may laginspiration slightly. This issue may become more pronounced in otherscenarios. However, the goal of providing humidity to the user duringinspiration while reducing humidity during other portions of the breathcycle may still be generally achieved. Moreover, should the timing ofdelivery of humidified gas to the user interface shift too far from theintended inspiratory phase, apparatus and methods as described hereinmay revert to the continuous modulation humidification mode until thesystem can again accurately provide the desired discontinuoushumidification mode. In still other embodiments, vapor delivery could besuspended entirely during a portion of the treatment period where suchsuspension would be beneficial.

As one may appreciate, these simulations illustrate exemplaryimplementations for predictive PAP humidification. When a sufficientnumber of these simulations are developed, a lookup table (containingscenario variables and their corresponding values for power intervaldelay and power interval duration) may be generated and stored in anactual PAP apparatus. During operation, the PAP apparatus controllersmay match the actual breath parameters to the lookup table to findappropriate values for power interval delay and duration. Alternatively,the methods described with respect to FIG. 21 may be used to calculatethese variables based on measured breath parameters in real-time.

While exemplary transfer function relationships between CFV power andvapor produced are referenced above (see, e.g., Equation 2), suchfunctional relationships may change to address the influence of variousfactors. For instance, it was discovered that the CFV is very responsivewhen the heater is maintained at a temperature just below itsvaporization temperature. Therefore, in order to maximize response time,it may be preferred to maintain power at a minimum threshold power level(e.g., hold power at 5 watts rather than terminating power altogether)and modulate power proportional to flow above that level during thepower interval. In other embodiments, the transfer function may deviatefrom strict modulation based upon the flow rate of the gas. For example,at the beginning of the power interval, it may be beneficial tomomentarily spike the power to a high level to introduce water vapormore quickly. The power level may then return to levels dictated by theflow modulation relationship.

In practice, accuracy of the simulation models could be confirmed andcorrected by including a humidity and temperature sensor in the mask toprovide a specific measurement of the humidity and temperature duringthe inspiratory portion of each breath cycle. By relaying thisinformation to the PAP controller and/or the humidification controller,humidification parameters may be tuned during PAP operation.

While described herein above in the context of a CPAP device, it iscontemplated that the same or similar algorithms utilized to time thedelivery of the humidified gas to the user interface could also beadapted to function with other PAP devices such as Bi-Level andAuto-titrating systems. At a minimum, computer algorithms may bemodified to utilize pressure as a variable rather than a constant inthese Bi-PAP and Auto-PAP systems.

U.S. Pat. No. 8,074,645 is incorporated herein by reference in itsentirety. Moreover, the complete disclosure of other patents, patentdocuments, and publications cited in the Background, the DetailedDescription of Exemplary Embodiments, and elsewhere herein areincorporated by reference in their entirety as if each were individuallyincorporated.

Illustrative embodiments are described and reference has been made topossible variations of the same. These and other variations,combinations, and modifications will be apparent to those skilled in theart, and it should be understood that this invention is not limited tothe illustrative embodiments set forth herein.

What is claimed is:
 1. A positive airway pressure apparatus comprising:a flow generator comprising a housing containing a blower, the bloweradapted to produce a flow of pressurized gas; a user interface adaptedto communicate the flow of pressurized gas to an airway during a breathcycle; an elongate delivery tube positioned between the flow generatorand the user interface, the delivery tube adapted to communicate theflow of pressurized gas from the blower to the user interface; ahumidifier defining an outlet that is in communication with the flow ofpressurized gas, the humidifier comprising a vaporizing device and awater source, the outlet located between the blower and the deliverytube; an electrical power source adapted to provide electrical power tothe humidifier; and a controller in communication with both thevaporizing device and the power source, the controller adapted toautomatically modulate the electrical power provided to the humidifierduring the breath cycle, wherein the electrical power is modulated inproportion to a flow rate of the flow of pressurized gas such that thehumidifier adds water vapor at a rate that maintains a near constanthumidity level in the flow of pressurized gas during the breath cycle.2. The apparatus of claim 1, wherein the controller is adapted tomodulate the electrical power provided to the humidifier based upon oneor more of: a pressure of the flow of pressurized gas; an intentionalleak; an unintentional leak; a breathing flow; a breath rate; aninspiratory tidal volume; an expiratory volume; an I:E ratio;inspiratory and expiratory flow dynamics; start and end of inspiration;start and end of expiration; time of peak flow during inspiration; timeof peak flow during expiration; ambient temperature; ambient humidity;an output power of the power source; a power-to-vaporization transferfunction of the vaporizing device; a volume of the delivery tube and theuser interface between the outlet of the vaporizing device and theairway; and a distance between the outlet of the vaporizing device andthe user interface.
 3. The apparatus of claim 1, wherein the humidifieris located within the housing of the flow generator.
 4. The apparatus ofclaim 1, wherein the controller is adapted to automatically modulate theelectrical power provided to the humidifier between: a minimum powerlevel; and a maximum power level.
 5. The apparatus of claim 4, whereinthe minimum power level is greater than zero watts.
 6. A positive airwaypressure apparatus comprising: a flow generator comprising a housingcontaining a blower, the blower adapted to produce a flow of pressurizedgas at a variable flow rate; a user interface adapted to communicate theflow of pressurized gas to an airway during a target breath cycle; anelongate delivery tube positioned between the flow generator and theuser interface, the delivery tube adapted to communicate the flow ofpressurized gas from the blower to the user interface; a humidifiercomprising a vaporizing device having an outlet in communication withthe flow of pressurized gas, the outlet located upstream from the userinterface; an electrical power source adapted to provide electricalpower to the vaporizing device; and a controller in communication withboth the power source and the vaporizing device, the controller adaptedto provide the electrical power to the vaporizing device during a powerinterval such that the vaporizing device introduces water vapor into aninspiration portion of the flow of pressurized gas, during the powerinterval, to produce a flow of pressurized gas with added humidity, andwherein a start time and duration of the power interval are selected orcalculated such that the flow of pressurized gas with added humidityarrives at the user interface beginning at or near an onset of aninspiratory phase of the target breath cycle and lasts for most or allof the inspiratory phase of the target breath cycle.
 7. The apparatus ofclaim 6, wherein the duration of the power interval is selected orcalculated by the controller to terminate the introduction of the watervapor by the vaporizing device such that the flow of pressurized gaswith added humidity that reaches the user interface ends at or near anend of the inspiratory phase or at or near an onset of an expiratoryphase of the target breath cycle.
 8. The apparatus of claim 6, whereinthe controller modulates power to the vaporizing device during the powerinterval to maintain a constant level of humidity within the flow ofpressurized gas with added humidity.
 9. The apparatus of claim 6,wherein the controller reduces the electrical power provided to thevaporizing device to a minimum level after the power interval expires.10. The apparatus of claim 6, wherein the outlet of the vaporizingdevice is located in the housing of the flow generator.
 11. Theapparatus of claim 6, wherein the controller is adapted to automaticallypredict when the onset of the inspiratory phase of the target breathcycle will begin based upon an analysis of one or more prior breathcycles.
 12. The apparatus of claim 8, wherein the controller is adaptedto modulate the electrical power provided to the vaporizing device basedupon one or more of: a pressure of the flow of pressurized gas; anintentional leak; an unintentional leak; a breathing flow; a breathrate; an inspiratory tidal volume; an expiratory volume; an I:E ratio;inspiratory and expiratory flow dynamics; start and end of inspiration;start and end of expiration; time of peak flow during inspiration; timeof peak flow during expiration; ambient temperature; ambient humidity;an output power of the power source; a power-to-vaporization transferfunction of the vaporizing device; and a distance between the outlet ofthe vaporizing device and the user interface.
 13. The apparatus of claim11, wherein the controller is adapted to predict when the inspiratoryportion of the flow of pressurized gas will reach the user interface byanalyzing one or more of: a pressure of the flow of pressurized gas; anintentional leak; an unintentional leak; a breathing flow; a breathrate; an inspiratory tidal volume; an expiratory volume; an I:E ratio;inspiratory and expiratory flow dynamics; start and end of inspiration;start and end of expiration; time of peak flow during inspiration; timeof peak flow during expiration; and a distance between the outlet of thevaporizing device and the user interface.
 14. A method for addinghumidity to gas delivered by a positive airway pressure apparatus, themethod comprising: producing, with a blower, a flow of pressurized gasat a variable flow rate; transporting the flow of pressurized gas fromthe blower to a user interface via a delivery tube positioned betweenthe blower and the user interface; detecting, with a controller, one orboth of an inspiratory phase and an expiratory phase of one or morebreath cycles; introducing, during a power interval, humidity into aportion of the flow of pressurized gas to produce a discrete flow ofpressurized gas with added humidity, the humidity introduced by avaporizing device having an outlet proximate the blower and incommunication with the flow of pressurized gas; and determining,automatically with the controller, a start time and duration of thepower interval so that the flow of pressurized gas with added humidityreaches the user interface at or near an onset of an inspiratory phaseof a current or future breath cycle and ends at or near an end of theinspiratory phase, or at or near an onset of an expiratory phase, of thecurrent or future breath cycle.
 15. The method of claim 14, furthercomprising introducing the humidity periodically into the flow ofpressurized gas to produce periodic flows of pressurized gas with addedhumidity, wherein each of the periodic flows of pressurized gas withadded humidity is timed to reach the user interface at or near the onsetof an inspiratory phase of one of the breath cycles.
 16. The method ofclaim 14, introducing the humidity into the flow of pressurized gas forthe power interval comprises providing electrical power to thevaporizing device during the power interval.
 17. The method of claim 16,wherein providing the electrical power to the vaporizing device duringthe power interval comprises modulating the electrical power to thevaporizing device during the power interval.
 18. The method of claim 14,wherein determining the start time and duration of the power intervalcomprises analyzing one or more characteristics of the one or morebreath cycles preceding the current or future breath cycle.
 19. Themethod of claim 14, wherein introducing the humidity into the portion ofthe flow of pressurized gas comprises introducing water vapor into theflow of pressurized gas at a variable rate proportional to a flow rateof the flow of pressurized gas.
 20. The method of claim 14, whereindetermining the start time and duration of the power interval comprisesselecting the start time and duration from a lookup table accessible bythe controller.
 21. The method of claim 14, wherein determining thestart time and duration of the power interval comprises calculating thestart time and duration with the controller.
 22. The method of claim 21,wherein calculating the start time and duration of the power intervalcomprises: measuring one or more characteristics of a previous breathcycle; determining ideal values of the start time and duration of thepower interval for the previous breath cycle; comparing the ideal valuesof the start time and duration of the power interval for the previousbreath cycle to actual values of the start time and duration used;calculating an error between the ideal values and the actual values ofthe start time and duration of the power interval for the previousbreath cycle; and predicting the start time and duration of the powerinterval for the current or future breath cycle based at least in partupon the error calculated.
 23. A method for adding humidity to gasprovided by a positive airway pressure (PAP) apparatus, the methodcomprising: producing a continuous and variable flow of pressurized gaswith a blower; transporting the flow of pressurized gas from the blowerto a user interface via a delivery tube positioned between the blowerand the user interface; predicting, automatically with a PAP controller,a start time and duration of an inspiratory phase of a target breathcycle based upon an analysis of a current or a preceding breath cycle;calculating or selecting, automatically with a humidificationcontroller, a delay time and duration of a power interval; providingpower, under control of the humidification controller, to a vaporizingdevice after expiration of the power interval delay time, the powerlasting for the power interval duration, wherein the vaporizing deviceis located proximate an outlet of the blower and is in communicationwith the flow of pressurized gas; introducing humidity with thevaporizing device into the flow of pressurized gas during the powerinterval duration to produce a flow of pressurized gas with addedhumidity that reaches the user interface at or near an onset of theinspiratory phase of the target breath cycle and terminates at or near abeginning of an expiratory phase of the target breath cycle.
 24. Themethod of claim 23, further comprising modulating the power provided tothe vaporizing device in proportion to a flow rate of the flow ofpressurized gas during the power interval duration such that a nearconstant humidity level is maintained in the flow of pressurized gaswith added humidity.
 25. The method of claim 23, wherein one or both ofthe delay time and duration of the power interval are selected based, atleast in part, upon one or more of: a pressure of the flow ofpressurized gas; an intentional leak; an unintentional leak; a breathingflow; a breath rate; an inspiratory tidal volume; an expiratory volume;an I:E ratio; inspiratory and expiratory flow dynamics; start and end ofinspiration; start and end of expiration; time of peak flow duringinspiration; time of peak flow during expiration; ambient temperature;ambient humidity; an output power available to the vaporizing device; apower-to-vaporization transfer function of the vaporizing device; and adistance between the outlet of the vaporizing device and the userinterface.